&Jui: 


y 


fly  permission  of 


Messrs.  Chance  Bros,  and  Co.,  Ltd. 

A  HUGE  LAMP 


The  marvellous  arrangement  of  lenses  and  prisms  which  enables  the 
lighthouse  to  send  out  its  guiding  flashes,  with  the  mechanism  for  turning  it. 
Made  for  "  Chilang  "  Lighthouse,  China 

Frontispiece 


MARVELS  OF 
SCIENTIFIC    INVENTION 


AN  INTERESTING  ACCOUNT  IN  NON-TECHNICAL  LANGUAGE 

OF  THE  INVENTION  OF  GUNS,  TORPEDOES,  SUBMARINES 

MINES,    UP-TO-DATE   SMELTING,   FREEZING,   COLOUR 

PHOTOGRAPHY,    AND    MANY    OTHER    RECENT 

DISCOVERIES    OF    SCIENCE 


BY 

THOMAS   W.  CORBIN 

AUTHOR  QF''"~™~*fc» 

"ENGINEERING  OF  TO-DAY,"  "MECHANICAL  INVENTIONS 

OF  TO-DAY,"  "THE  ROMANCE  OF  SUBMARINE 

ENGINEERING,"  &>£.,  &C. 


WITH    32    ILLUSTRATIONS   6^   DIAGRAMS 


PHILADELPHIA 
J.    B.    LIPPINCOTT    COMPANY 

LONDON  :  SEELEY,  SERVICE  fc»  CO.  LTD. 


CONTENTS 

CHAPTER  PAGE 

I.  DIGGING  WITH  DYNAMITE  ....         9 

II.  MEASURING  ELECTRICITY  .             .             .             .22 

III.  THE  FUEL  OF  THE  FUTURE  .             .             .             .42 

IV.  SOME  VALUABLE  ELECTRICAL  PROCESSES            .             .55 
V.  MACHINE-MADE  COLD   .  .             .             .             .67 

VI.  SCIENTIFIC  INVENTIONS  AT  SEA  .  .  .78 

VII.  THE  GYRO-COMPASS      .  .  .  .  .90 

VIII.  TORPEDOES  AND  SUBMARINE  MINES      .  .  .98 

IX.  GOLD  RECOVERY  .  .  .  .  .109 

X.  INTENSE  HEAT  .  .  .  .  .123 

XI.  AN  ARTIFICIAL  COAL  MINE     .  .  .  .137 

XII.  THE  MOST  STRIKING  INVENTION  OF  RECENT  TIMES  .     149 

XIII.  How  PICTURES  CAN  BE  SENT  BY  WIRE  .  .176 

XIV.  A  WONDERFUL  EXAMPLE  OF  SCIENCE  AND  SKILL  .     191 
XV.  SCIENTIFIC  TESTING  AND  MEASURING   .             .  .198 

XVI.  COLOUR  PHOTOGRAPHY  .  .  .  .212 

XVII.  How  SCIENCE  AIDS  THE  STRICKEN  COLLIER     .  .     220 

XVIII.  How  SCIENCE  HELPS  TO  KEEP  us  WELL  .  .     231 

XIX.  MODERN  ARTILLERY     .....     236 

APPENDIX          ......     245 

INDEX  .......     247 


LIST   OF   ILLUSTRATIONS 


A  Huge  Lamp 

First  Effect  of  the  Dynamite   . 

A  Fine  Crop     .... 

Apple-tree  planted  by  Spade  . 

Machine-made  Ice 

A  Cold  Store    .... 

Dassen  Island  Lighthouse 

Measuring  Heat 

The  Telewriter 

A  Miners'  Rescue  Team 

Pneumatic  Hammer  Drill 

An  Artificial  Coal  Mine 

Sectional  view  of  a  60-pounder  Gun    . 

Rifles  of  different  Nations 


Frontispiece 

FACING  PAGE 

.      16 

24 
48 

.  72 
80 
88 

.  128 
.  184 
.  208 
.  216 
.  224 
.  232 
240 


DIAGRAMS 


1 .  Principle  of  Galvanometer 

2.  String  Galvanometer 

3.  Duddell  Therm  o-Galvanometer 

7 


PAGB 

30 
31 
39 


8  DIAGRAMS 

FIG.  PAGE 

4.  Construction  of  a  Voltmeter          .  .  .  .64 

5.  The  Working  of  a  Refrigerating  Machine  .  .       70 

6.  Hertz's  Machine    .             ,             .  .  .  .155 

7.  Hertz  "Detector"             .             .  .  .  .156 

8.  9.  10.  Wireless  Waves        .             .  .  .  .158 

11.  A  Wireless  Antenna          .             .  .  .  .164 

12.  Poulsen's  Machine             .             .  .  .  .166 

13.  14.  How  Pictures  are  sent  by  Wire  .  .  .177 
1 5.  Message  received  by  Telewriter    .  .  .  .189 


MARVELS  OF  SCIENTIFIC 
INVENTION 

CHAPTER  I 

DIGGING  WITH  DYNAMITE 

MOST  people  are  afraid  of  the  word  explosion  and 
shudder  with  apprehension  at  the  mention  of 
dynamite.  The  latter,  particularly,  conjures  up 
visions  of  anarchists,  bombs,  and  all  manner  of  wickedness. 
Yet  the  time  seems  to  be  coming  when  every  farmer  will 
regard  explosives,  of  the  general  type  known  to  the  public 
as  dynamite,  as  among  his  most  trusty  implements.  It  is 
so  already  in  some  places.  In  the  United  States  explosives 
have  been  used  for  years,  owing  to  the  exertions  of  the 
Du  Pont  Powder  Company,  while  Messrs  Curtiss'  and  Harvey, 
and  Messrs  Nobels,  the  great  explosive  manufacturers,  are 
busy  introducing  them  in  Great  Britain. 

It  will  perhaps  be  interesting  first  of  all  to  see  what  this 
terror-striking  compound  is.  One  essential  feature  is  the 
harmless  gas  which  constitutes  the  bulk  of  our  atmosphere, 
nitrogen.  Ordinarily  one  of  the  most  lazy,  inactive,  inert 
of  substances,  this  gas  will,  under  certain  circumstances, 
enter  into  combination  with  others,  and  when  it  does  so 
it  becomes  in  some  cases  the  very  reverse  of  its  usual 
peaceful,  lethargic  self.  It  is  as  if  it  entered  reluctantly 
into  these  compounds  and  so  introduced  an  element  of 
instability  into  them.  It  is  like  a  dissatisfied  partner  in  a 
business,  ready  to  break  up  the  whole  combination  on  very 
slight  provocation. 

And  it  must  be  remembered  that  an  explosive  is  simply 
some  chemical  compound  which  can  change  suddenly  into 

9 


10  DIGGING  WITH  DYNAMITE 

something  else  of  much  larger  volume.  Water,  when  boiled, 
increases  to  about  1600  times  its  own  volume  of  steam,  and 
if  it  were  possible  to  bring  about  the  change  suddenly  water 
would  be  a  fairly  powerful  explosive.  Coal  burnt  in  a  fire 
changes,  with  oxygen  from  the  atmosphere,  into  carbonic  acid 
gas,  and  the  volume  of  that  latter  which  is  so  produced  is 
much  more  than  that  of  the  combined  volumes  of  the  oxygen 
and  coal.  When  the  burning  takes  place  in  a  grate  or  furnace 
we  see  nothing  at  all  like  an  explosion,  for  the  simple  reason 
that  the  change  takes  place  gradually.  That  is  necessarily  so 
since  the  coal  and  oxygen  are  only  in  contact  at  the  surface 
of  the  former.  If,  however,  we  grind  the  coal  to  a  very  fine 
powder  and  mix  it  well  with  air,  then  each  fine  particle  is 
in  contact  with  oxygen  and  can  burn  instantly.  Hence  coal- 
dust  in  air  is  an  explosive.  It  used  to  be  thought  that  colliery 
accidents  were  due  entirely  to  the  explosion  of  methane,  a 
gas  which  is  given  off  by  the  coal,  but  it  has  of  recent  years 
dawned  upon  people  that  it  is  the  coal-dust  in  the  mine  which 
really  does  the  damage.  The  explosion  of  methane  stirs  up 
the  dust,  which  then  explodes.  The  former  is  comparatively 
harmless,  but  it  acts  as  the  trigger  or  detonator  which  lets 
loose  the  force  pent  up  in  the  innocent-looking  coal-dust. 
Hence  the  greatest  efforts  in  modern  collieries  are  bent 
towards  ridding  the  workings  of  dust  or  else  damping  it  or 
in  some  other  way  preventing  it  from  being  stirred  up  into 
the  dangerous  state. 

So  the  essential  feature  of  any  explosive  is  oxygen  and 
something  which  will  burn  with  it.  If  it  be  a  solid  or  liquid 
the  oxygen  must  be  a  part  of  the  combination  or  mixture, 
for  it  cannot  get  air  from  the  surrounding  atmosphere  quickly 
enough  to  explode  ;  and,  moreover,  it  is  generally  necessary 
that  explosives  should  work  in  a  confined  space  away  from 
all  contact  with  air.  So  oxygen,  of  necessity,  must  be  an 
integral  part  of  the  stuff  itself.  But  when  oxygen  combines 
with  anything  it  usually  clings  rather  tenaciously  to  its  place 
in  the  compound  and  is  not  easily  disturbed  quickly,  and 
that  is  where  the  nitrogen  seems  to  find  its  part.  It  supplies 


DIGGING  WITH  DYNAMITE  11 

the  disturbing  element  in  what  would  otherwise  be  a 
harmonious  combination,  so  that  the  oxygen  and  the 
burnable  substances  readily  split  up  and  form  a  new 
combination,  with  the  nitrogen  left  out. 

Of  all  the  harmless  things  in  the  world  one  would  think 
that  that  sweet,  sticky  fluid,  glycerine,  which  most  of  us  have 
used  at  one  time  or  another  to  lubricate  a  sore  throat,  was 
the  most  harmless.  As  it  stands  in  its  bottle  upon  the 
domestic  medicine  shelf,  who  would  suspect  that  it  is  the 
basis  of  such  a  thing  as  dynamite  ? 

Such  is  the  case,  however,  for  glycerine  on  being  brought 
into  contact  with  a  mixture  of  sulphuric  and  nitric  acids 
gives  birth  to  nitro-glycerine,  an  explosive  of  such  sensitivity, 
of  such  a  furious,  violent  nature,  that  it  is  never  allowed  to 
remain  long  in  its  primitive  condition,  but  is  as  quickly  as 
possible  changed  into  something  less  excitable. 

Glycerine  is  one  of  those  organic  compounds  which  is 
obtained  from  once-living  matter.  Arising  as  a  by-product 
in  the  manufacture  of  soap,  it  consists,  as  do  so  many  of 
the  organic  substances,  of  carbon  and  hydrogen,  the  atoms 
of  which  are  peculiarly  arranged  to  form  the  glycerine 
molecule.  To  this  the  nitric  acid  adds  oxygen  and  nitrogen, 
the  sulphuric  acid  simply  standing  by,  as  it  were,  and 
removing  the  surplus  water  which  arises  during  the  process. 
So  while  glycerine  is  carbon  and  hydrogen,  nitro-glycerine 
is  carbon,  hydrogen,  nitrogen  and  oxygen.  In  this  state 
they  form  a  compact  liquid,  which  occupies  little  space. 

The  least  thing  upsets  them,  however.  The  carbon 
combines  with  oxygen  into  carbon  dioxide,  commonly  called 
carbonic  acid  gas,  the  hydrogen  and  some  more  oxygen 
form  steam,  while  the  nitrogen  is  left  out  in  the  cold,  so  to 
speak.  And  the  total  volume  of  the  gases  so  produced  is 
about  6000  times  that  of  the  original  liquid.  It  is  easy  to 
see  that  a  substance  which  is  liable  suddenly  to  increase  its 
volume  by  6000  times  is  an  explosive  of  no  mean  order. 

But  the  fact  that  it  is  liable  to  make  this  change  on 
a  comparatively  slight  increase  in  temperature  or  after  a 


12  DIGGING  WITH  DYNAMITE 

concussion  makes  it  too  dangerous  for  practical  use.  It 
needs  to  be  tamed  down  somewhat.  This  was  first  done 
by  the  famous  Nobel,  who  mixed  it  with  a  fine  earth  known 
as  kieselguhr,  whereby  its  sensitiveness  was  much  decreased. 
This  mixture  is  dynamite. 

It  will  be  seen  that  the  function  of  the  "  earth  "  is  simply 
to  act  as  an  absorbent  of  the  liquid  nitro-glycerine,  and 
several  other  things  can  be  used  for  the  same  purpose. 
Moreover,  there  are  now  many  explosives  of  the  dynamite 
nature  but  differing  from  it  in  having  an  active  instead  of 
a  passive  absorbent,  so  that  the  decrease  in  sensitivity  is 
accompanied  by  an  increase  in  strength.  For  example, 
gelignite,  which  is  being  used  for  agricultural  purposes  in 
Great  Britain,  consists  of  nitro-glycerine  mixed  with  nitro- 
cotton,  wood-meal  and  saltpetre.  The  wood-meal  acts  as 
the  absorbent  instead  of  the  kieselguhr,  while  the  nitro- 
cotton  is  another  kind  of  explosive  and  the  saltpetre,  one 
of  the  ingredients  in  the  old  gunpowder,  provides  the  neces- 
sary oxygen  for  burning  up  the  wood-meal.  Nitro-cotton  is 
made  in  much  the  same  way  as  nitro-glycerine,  except  that 
cotton  takes  the  place  of  the  glycerine.  Cotton  is  almost 
pure  cellulose,  another  organic  substance,  like  glycerine 
insomuch  as  it  is  composed  of  carbon  and  hydrogen,  but, 
unlike  it,  containing  also  oxygen.  Treated  with  nitric  acid 
it  also  forms  a  combination  of  carbon,  hydrogen,  oxygen 
and  nitrogen,  which  is  called  nitro-cotton,  nitro-cellulose,  or 
gun-cotton. 

It  may  be  asked,  why,  if  these  two  substances  are  thus 
similar,  need  they  be  mixed  ?  The  answer  is  that  although 
alike  to  a  certain  degree  they  are  not  exactly  the  same, 
and  the  modern  manufacturer  of  explosives  in  his  strife 
after  perfection  finds  that  for  certain  purposes  one  is  the 
best,  and  for  others  another,  while  for  others  again  a 
combination  may  excel  any  single  one. 

For  some  work  another  kind  of  explosive  altogether  is 
to  be  preferred.  This  is  based  upon  chlorate  of  potash, 
a  compound  very  rich  in  oxygen,  which  it  is  prepared  to  give 


DIGGING  WITH  DYNAMITE  13 

up  readily  to  burn  any  other  suitable  element  which  may  be 
at  hand.  A  well-known  explosive  of  this  class  is  that  known 
as  cheddite,  since  it  was  first  made  at  a  factory  at  Chedde, 
in  Savoy. 

For  the  sake  of  simplicity,  however,  I  propose  in  the 
following  descriptions  to  refer  to  all  these  explosives  under 
the  common  term  "  dynamite,"  since  that  will  probably 
convey  to  the  general  public  an  idea  of  their  nature  better 
than  any  other  term  or  terms  which  I  could  choose. 

So  now  we  come  to  the  great  question,  how  can  the 
modern  farmer  benefit  by  the  use  of  high  explosives  such  as 
these  ?  The  answer  is,  in  many  ways.  Let  us  take  the 
most  obvious  one  first. 

A  farmer  has  been  ploughing  his  land  and  growing  his 
crops  upon  it  for  years.  Perchance  his  forefathers  have 
been  doing  the  same  for  generations.  Every  year,  for 
centuries  possibly,  a  hard  steel  ploughshare  has  gone  over 
that  ground,  turning  over  and  over  the  top  soil  to  a  depth 
of  six  to  eight  inches.  Each  season  the  plants,  whatever 
they  may  be,  grow  mainly  in  that  top  layer.  They  take  the 
goodness  or  nourishment  out  of  it  and  it  eventually  becomes 
more  or  less  sterile.  By  properly  rotating  his  crops  he 
mitigates  this  to  a  certain  extent,  in  addition  to  which  he 
restores  to  the  land  some  of  its  old  nitrogenous  constituents 
by  the  addition  of  manure.  Yet,  do  what  he  will,  this  thin 
top  layer  is  bound  to  become  exhausted.  And  all  the  while 
a  few  inches  lower  down  there  is  almost  virgin  soil  which  has 
scarcely  been  disturbed  since  the  creation  of  the  world. 

Nay,  more,  that  virgin  soil,  with  all  its  plant  food  still 
in  it,  is  not  only  doing  little  for  its  owner,  it  is  positively 
doing  him  harm.  For  every  time  his  plough  goes  over 
it  it  tends  to  ram  it  down  flat ;  every  time  a  man  walks 
over  it  the  result  is  the  same;  every  horse  that  passes, 
everything  that  happens  or  has  happened  for  centuries 
in  that  field,  tends  to  make  that  soil  just  below  the  reach 
of  the  ploughshare  a  hard,  impervious  mass,  through  which 
only  the  roots  of  the  most  strongly  growing  plants  can  find 


14  DIGGING  WITH  DYNAMITE 

a  way,  and  which  tends  to  make  the  soil  above  it  wet  in 
wet  weather  and  dry  in  dry  weather.  Thus  roots  have  to 
spread  sideways  instead  of  downwards  ;  or,  growing  down- 
wards with  difficulty,  each  plant  has  to  expend  vital  energy 
in  forcing  its  roots  through  the  hard  ground  which  it  might 
better  employ  in  producing  flowers  or  fruits.  And  there  is 
no  natural  storage  of  water.  A  shower  drenches  the  ground. 
In  time  it  dries,  through  evaporation  into  the  air,  and  then 
when  the  drought  comes  all  is  arid  as  the  Sahara. 

That  hard  subsoil  is  known  by  the  term  "  hard-pan,"  and, 
as  we  have  seen,  it  is  produced  more  or  less  by  all  that  goes 
on  in  the  field.  Even  worse  is  the  case — a  very  frequent  one 
too — wherein  there  is  a  natural  stratum  of  clay  or  equally 
dense  waterproof  material  lying  a  few  feet  down. 

Beyond  the  reach  of  any  plough,  this  hard  stratum  can 
be  broken  up  by  the  use  of  dynamite.  The  usual  method  is 
to  drive  holes  in  the  ground  about  fifteen  to  twenty  feet 
apart  and  about  three  or  four  feet  deep,  right  into  the  heart 
of  the  hard  layer.  At  the  bottom  of  each  hole  is  placed  a 
cartridge  of  dynamite  with  a  fuse  and  a  detonator.  This 
latter  is  a  small  tube  containing  a  small  quantity  of  explosive 
which,  unlike  the  dynamite,  can  be  easily  fired,  and  initiates 
the  detonation  of  the  cartridge. 

When  these  miniature  earthquakes  have  taken  place  all 
over  a  field  a  very  different  state  of  things  prevails.  The 
"  hard-pan "  has  been  broken.  The  explosive  used  for 
such  a  purpose  has  a  sudden  shattering  power,  whereby  it 
pulverises  the  ground  in  its  vicinity  rather  than  making  a 
great  upheaval  at  the  surface.  The  sudden  shock  makes 
cracks  and  fissures  in  all  directions,  through  which  roots  can 
easily  make  their  way.  Moreover,  it  permits  air  to  find  an 
entrance,  thereby  aerating  the  soil  in  such  a  way  as  to  increase 
its  fertility.  The  heat,  or  else  the  chemical  products  of  the 
explosion,  seem  to  destroy  the  fungus  germs  in  the  ground. 
Finally  a  natural  storage  of  water  is  set  up.  Heavy  rain, 
instead  of  drenching  the  upper  soil,  simply  moistens  it  nicely, 
while  the  surplus  water  descends  into  the  newly  disturbed 


DIGGING  WITH  DYNAMITE  15 

layers,  there  to  remain  until  the  roots  pump  it  up  in  time  of 
drought. 

It  is  stated  that  an  acre  of  hay  pumps  up  out  of  the  soil 
500  tons  of  water  per  annum,  so  it  is  easy  to  see  what 
an  important  feature  this  natural  water-storage  is. 

Farmers  say  that  their  crops  have  doubled  in  value  after 
thus  dynamiting  the  subsoil. 

This  operation  has  been  spoken  of  as  a  substitute  for 
ploughing,  but  that  may  be  put  down  to  "  journalistic 
licence,"  for  while  it  truly  conveys  the  general  idea,  it  is 
hardly  correct.  The  ordinary  plough  turns  over  about 
eight  inches,  the  special  subsoil  plough  reaches  down  to 
about  eighteen  inches,  but  the  dynamite  method  loosens 
the  ground  to  a  depth  of  six  or  seven  feet.  Corn  roots  if 
given  a  chance  will  go  downwards  from  four  to  eight  feet. 
Potatoes  go  down  three  feet,  hops  eight  to  eighteen  feet 
and  vines  twenty  feet,  so  it  is  easy  to  see  how  restricted  the 
plants  are  when  their  natural  rooting  instincts  are  restrained 
by  a  hard  layer  at  a  depth  of  eighteen  inches  or  so. 

The  holes  are  made  by  means  of  a  bar  or  drill.  A  great 
deal  depends,  of  course,  upon  the  hardness  of  the  soil.  Some- 
times a  steel  bar  has  to  be  driven  in  by  a  sledge-hammer. 
At  others  a  pointed  bar  can  be  pushed  down  by  hand.  In 
some  cases  it  will  be  found  that  the  best  tool  to  employ  is 
a  "  dirt-auger,"  a  tool  like  a  carpenter's  auger,  which  on 
being  turned  round  and  round  bores  its  way  into  the  earth. 
However  it  may  be  done,  one  or  more  cartridges  of  dynamite 
are  lowered  into  the  finished  hole,  one  of  them  being  fitted 
with  the  necessary  detonator  and  fuse.  Then  a  little  loose 
earth  or  sand  is  dropped  into  the  hole  until  it  is  filled  to  a 
depth  of  six  inches  or  so  above  the  uppermost  cartridge. 
Above  that  it  is  quite  safe  to  fill  the  hole  with  earth,  ramming 
it  in  with  a  wooden  rammer.  This  is  called  "tamping," 
and  it  is  necessary  in  order  to  prevent  the  force  of  the 
explosion  being  wasted  in  simply  blowing  up  the  hole. 
What  is  wanted  is  that  the  explosion  shall  take  place  within 
an  enclosed  chamber  so  that  its  effect  may  be  felt  equally 


16  DIGGING  WITH  DYNAMITE 

in  all  directions.     The  holes  are  generally  about  an  inch  and 
a  half  or  an  inch  and  three-quarters  in  diameter. 

There  are  two  ways  of  firing  the  charges.  One  is  by  means 
of  fuses.  The  detonator  is  fastened  to  one  cartridge  and  a 
length  of  fuse  is  attached  to  the  detonator,  which  passing 
up  the  hole  terminates  above  the  ground.  The  fuse  is  a 
tube  of  cotton  filled  with  gunpowder,  and  it  burns  at  the 
rate  of  about  two  feet  a  minute.  Thus  if  three  feet  of  fuse 
be  used  the  man  who  lights  it  has  a  minute  and  a  half  in 
which  to  find  a  place  of  safety  from  falling  stones. 

The  other  way  is  by  electricity.  In  this  case  an  electric 
fuse  is  attached  to  the  cartridge  and  two  wires  are  led  up 
the  hole.  These  are  connected  to  an  electrical  machine, 
which  causes  a  current  to  pass  down  into  the  fuse,  where,  by 
heating  a  fine  platinum  wire,  it  fires  the  detonating  material 
with  which  it  is  packed.  This  detonating  material  in  turn 
fires  the  dynamite. 

The  advantage  of  the  electrical  method  is  that  twenty  or 
thirty  holes  being  simultaneously  connected  to  the  same 
machine  can  all  be  fired  at  once. 

And  now  let  us  think  of  another  kind  of  farming,  in  which 
fruit  trees  are  concerned.  With  a  large  tree  the  need  of 
plenty  of  underground  space  for  its  roots  would  seem  to  be 
more  important  even  than  in  the  case  of  annual  plants  like 
wheat.  Yet  we  know  very  well  that  the  usual  procedure 
is  to  dig  a  small  hole  just  about  big  enough  to  accommodate 
the  roots  of  the  sapling  when  it  is  planted,  while  the  ground 
all  round  is  left  undisturbed.  The  assumption  is  that  the 
tree  will,  in  time,  be  able  to  push  its  roots  through  anything 
which  is  not  actually  solid  rock.  So  much  is  this  the  case 
that  one  authority  has  thought  fit  to  warn  tree-growers  in 
this  picturesque  fashion.  "  When  planting  a  tree,"  he  says, 
"  forget  what  it  is  you  are  doing,  and  think  that  you  are 
about  to  bury  the  biggest  horse  you  know."  How  many 
people  when  planting  any  tree  dig  a  hole  big  enough  to  bury 
a  horse  ?  It  is  fairly  safe  to  reply,  only  those  who  do  it  by 
dynamite. 


DIGGING  WITH  DYNAMITE  17 

The  method  of  working  is  to  bore  a  hole  nearly  as  deep  as 
the  hole  you  want  to  blast.  At  the  bottom  place  a  powerful 
charge,  far  stronger  than  you  would  use  for  "  subsoiling," 
as  just  described.  That  will  not  only  blow  a  hole  big  enough 
for  you  to  put  your  tree  in,  but  it  will  loosen  the  ground  all 
around  the  hole  for  yards.  The  main  debris  from  the  hole 
will  fall  back  into  it,  but  that  will  not  matter  much,  since, 
being  all  loose,  it  is  an  easy  matter  to  remove  as  much  as  is 
necessary  to  plant  the  young  tree.  The  advantages  are  the 
same  as  those  enumerated  in  the  previous  case — namely, 
the  loosened  ground  gives  more  scope  for  the  roots — apple- 
tree  roots  want  twenty  feet  or  so — the  ground  holds  moisture 
better,  and  the  explosion  kills  the  fungus  germs.  In  addition 
to  these  there  is  the  advantage  that  to  blast  a  hole  like  this 
is  cheaper  than  digging  it. 

And  that  the  advantages  are  not  merely  theoretical  is 
shown  by  the  fact  that  trees  so  planted  actually  do  grow 
stronger,  bigger  and  quicker  than  precisely  similar  ones  under 
the  same  conditions,  but  set  in  the  ordinary  way  with  a 
spade. 

And  not  only  do  new  trees  thus  benefit ;  old  trees  can  be 
helped  by  dynamite.  Many  an  existing  orchard  has  been 
improved  by  exploding  dynamite  at  intervals  between  the 
rows  of  trees.  Care  has  to  be  taken  to  see  that  the  disturb- 
ance is  not  so  violent  or  so  close  as  to  damage  the  trees,  but 
that  can  be  easily  arranged,  and  then  the  result  is  that  the 
soil  all  around  the  trees  is  loosened,  the  roots  are  given  more 
freedom  and  the  water-storing  properties  of  the  ground 
are  greatly  improved. 

Again,  how  often  a  farmer  is  troubled  with  a  pond  or  a 
patch  of  marshy  ground  right  in  the  midst  of  his  fields. 
It  is  of  no  use,  and  simply  serves  to  make  the  field  in  which 
it  occurs  more  difficult  to  plough  and  to  cultivate — besides 
being  so  much  good  land  wasted.  Now  the  reason  for  the 
existence  of  that  pond  or  marsh  is  that  underneath  the 
surface  there  is  an  impervious  layer  in  which,  as  in  a  basin, 
the  water  can  collect.  Make  a  hole  in  that  and  it  will  no 


18  DIGGING  WITH  DYNAMITE 

more  hold  water  than  a  cracked  jug  will.     And  to  make 
that  hole  with  dynamite  is  the  easiest  thing  in  the  world. 

If  the  pond  be  merely  a  collection  of  water  which  occurs 
in  wet  weather,  but  which  dries  up  quickly,  there  simply 
needs  to  be  drilled  a  deep  hole  and  a  fairly  strong  explosion 
caused  at  the  bottom  of  it.  How  deep  the  hole  must  be 
depends  upon  the  formation  of  the  earth  at  that  point,  and 
how  low  down  is  the  stratum  which,  being  waterproof,  causes 
the  water  to  remain.  It  is  that,  of  course,  which  must  be 
broken  through,  and  so  the  explosion  must  be  caused  at  a 
point  near  the  under  side  of  that  layer.  With  a  little  experi- 
ence the  operator  can  judge  the  position  by  the  feel  of  the 
tool  with  which  he  makes  the  hole.  If  the  pond  is  permanent 
but  shallow,  men  can  wade  to  about  the  centre,  there  to  drill 
a  hole  and  fire  a  shot.  If  it  be  permanent  and  deep,  then  the 
work  must  be  done  from  a  raft,  which,  however,  can  be  easily 
constructed  for  the  purpose.  Once  broken  through,  the 
water  will  quickly  pass  away  below  the  impervious  stratum 
and  useless  land  will  become  valuable. 

The  same  may  be  done  on  a  larger  scale  by  blasting  ditches 
with  dynamite.  This  is  in  many  cases  much  cheaper  than 
digging  them.  A  row  of  holes  is  put  down,  or  even  two 
or  three  rows,  according  to  the  width  of  the  proposed  ditch. 
In  depth  they  are  made  a  little  less  than  the  depth  of  the 
ditch  that  is  to  be.  And  for  a  reason  which  will  be  apparent 
they  are  put  very  close  together,  say  three  feet  or  so  apart. 
Preparations  may  thus  be  made  for  blasting  a  ditch  hundreds 
of  feet  long  and  then  all  are  fired  together.  The  earth  is 
thrown  up  by  a  mighty  upheaval,  a  ditch  being  produced 
of  remarkable  regularity  considering  the  means  by  which 
it  is  made.  The  sides,  of  course,  take  a  nice  slope,  the  debris 
is  thrown  away  on  both  sides  and  spread  to  a  considerable 
distance,  so  that,  given  favourable  conditions  and  a  well- 
arranged  explosion,  there  is  constructed  a  finished  ditch 
which  hardly  needs  touching  with  spade  or  other  tool. 

It  not  being  feasible  to  fire  a  lot  of  holes  electrically,  the 
limit  being  about  thirty,  the  simultaneous  explosion  of 


DIGGING  WITH  DYNAMITE  19 

perhaps  hundreds  has  to  be  brought  about  in  some  other 
manner,  and  usually  it  is  accomplished  by  the  simple  device 
of  putting  the  holes  fairly  near  together  and  firing  one  with 
a  fuse.  The  commotion  set  up  by  this  one  causes  the  nearest 
ones  to  "go  off,"  they  in  turn  detonating  those  farther  on, 
with  the  result  that  explosion  follows  explosion  all  along 
the  line  so  rapidly  as  to  be  almost  instantaneous. 

A  farmer  who  is  troubled  by  a  winding  stream  passing 
through  his  land,  cutting  it  up  into  awkward  shapes,  can 
straighten  it  by  blasting  a  ditch  across  a  loop  in  the  manner 
just  described.  In  the  case  of  low-lying  land,  however, 
ditches  are  obviously  no  use,  since  water  would  not  flow 
away  along  them.  In  that  case  the  principle  suggested  just 
now  for  dealing  with  an  inconvenient  pond  can  sometimes 
be  used,  for  if  the  subsoil  be  blasted  through  at  several 
points  it  is  very  likely  that  water  will  find  a  way  downwards 
by  some  means  or  other. 

And  the  list  of  possible  uses  is  by  no  means  exhausted  yet. 
A  man  opening  up  virgin  land  often  finds  old  tree  stumps 
his  greatest  bother.  He  can  dig  round  them  and  then  pull 
them  out  with  a  team  of  horses,  but  by  far  the  simpler  way 
is  with  a  few  well-placed  dynamite  cartridges,  for  they  not 
only  throw  up  the  stump  for  him,  but  they  break  it  up, 
shake  the  earth  from  it,  and  leave  it  ready  for  him  to  cart 
away  or  to  burn. 

Boulders,  too,  can  be  blown  to  pieces  far  more  easily 
than  one  would  think.  The  charges  may  be  put  underneath 
them  as  with  the  tree  stumps,  but  in  many  cases  that  is  not 
necessary,  all  that  is  needed  being  some  dynamite  laid  upon 
the  top  of  the  rock  and  covered  with  a  heap  of  clay.  So 
sudden  is  the  action  of  the  explosive  that  its  shock  will 
break  up  the  stone  underneath  it.  Yet  another  way, 
perhaps  the  most  effective  of  all,  is  to  drill  a  hole  into  the 
stone  and  fire  a  charge  inside  it.  It  behoves  the  onlooker 
then  to  keep  away,  for  the  fragments  may  be  thrown  three 
or  four  hundred  feet,  a  fair  proof  that  the  stone  will  be 
very  thoroughly  demolished. 


20  DIGGING  WITH  DYNAMITE 

Even  in  the  digging  of  wells  explosives  may  be  useful. 
In  that  case  the  holes  are  made  in  a  circle,  and  they  slant 
downwards  and  inwards,  so  that  their  lower  ends  tend  to 
meet.  The  result  of  simultaneously  exploding  the  charges 
in  these  holes  is  to  cut  out  a  conical  hole  a  little  larger  in 
size  than  the  ring  and  a  little  deeper  than  the  point  at  which 
the  explosion  took  place.  The  bottom  of  that  hole  can  be 
levelled  a  little  and  the  operation  repeated,  and  so  stage 
by  stage  the  well  will  proceed  to  grow  downwards. 

The  thought  that  naturally  occurs  to  one  is  this.  All  the 
operations  described  may  be  very  well,  the  cost  may  be  low, 
and  the  effect  good,  but  are  they  sufficient  to  compensate  for 
the  risks  necessarily  dependent  upon  the  use  of  explosives  ? 
The  doubt  implied  in  that  question,  natural  though  it  be, 
is  based  upon  prejudice,  with  which  we  are  all  more  or  less 
afflicted.  The  art  of  making  these  explosive  substances  has 
been  brought  to  such  a  pitch  that  with  reasonable  care 
there  is  no  risk  whatever.  The  greatest  possible  care  is 
used  in  the  factory  to  see  that  all  explosives  sent  out  are 
what  they  are  meant  to  be,  and  that  they  can  therefore  be 
relied  upon  to  behave  according  to  programme  and  not  to 
play  any  tricks.  That  is  the  first  step,  and  what  with 
competition  between  makers,  Government  inspection,  and 
searching  inquiry  into  the  slightest  accident,  and  the  desire 
of  each  maker  to  keep  up  the  credit  of  his  name,  it  is  safe 
to  say  that  modern  explosives  may  be  relied  upon  to  do  their 
duty  faithfully.  The  second  step  in  the  process  of  securing 
safety  is  that  the  powerful  explosive,  the  one  that  does  the 
work,  is  made  very  insensitive,  so  that  it  is  really  quite  hard 
to  explode  it.  With  reasonable  care,  then,  it  will  never  go 
off  by  accident.  On  the  other  hand,  the  sensitive  material, 
which  is  easy  to  "  let  off,"  is  in  very  small  quantities,  so 
small  that  an  accident  with  it  would  not,  again  with 
reasonable  precautions,  be  a  serious  matter. 

Fuse,  too,  is  very  reliable  nowadays.  The  man  who  lights 
the  fuse  may  be  absolutely  sure  that  he  will  have  that  time 
to  get  to  a  place  of  safety  which  corresponds  to  the  length 


DIGGING  WITH  DYNAMITE  21 

of  fuse  which  he  employs.  With  electrical  firing,  too,  it  is 
quite  easy  to  arrange  that  the  final  electrical  connection 
shall  not  be  made  until  all  are  at  a  safe  distance,  so  that  a 
premature  explosion  is  impossible. 

In  many  of  the  cases  described,  the  shock  takes  place 
almost  entirely  within  the  earth  and  there  is  very  little 
debris  thrown  about. 

Indeed  the  only  danger  which  is  to  be  feared  with  these 
operations  is  about  on  a  par  with  that  which  every  farm 
hand  runs  from  the  kick  of  a  horse.  Any  careful,  trust- 
worthy man  could  be  quite  safely  taught  to  do  this  work, 
and  with  the  assistance  of  a  labourer  he  could  do  all  that 
is  necessary.  Given  a  fair  amount  of  intelligence,  too,  he 
would  take  but  little  teaching.  Altogether  there  is  no  doubt 
that  the  use  of  explosives  is  going  to  have  a  marked  effect 
upon  farming  operations  in  the  near  future. 


CHAPTER  II 

MEASURING  ELECTRICITY 

THERE  are  many  people  whose  acquaintance  with 
electricity  consists  mainly  in  paying  the  electric 
light  bill.     To  such  the  instruments  whereby  elec- 
tricity is  measured  will  make  a  specially  interesting  appeal. 

Current  is  sold  in  Great  Britain  at  so  much  per  Board  of 
Trade  Unit.  To  state  what  that  is  needs  a  preliminary 
explanation  of  the  other  units  employed  in  connection 
with  electric  currents. 

The  public  electricity  supply  in  any  district  is  announced 
to  be  so  many  volts,  it  may  be  100,  200  or  perhaps 
230,  but  whatever  it  be,  it  is  always  so  many  "  volts." 
Then  the  electrician  speaks  lightly  of  numbers  of 
"  amperes,"  he  may  even  talk  of  the  number  of  "  watts  " 
used  by  the  lamps,  while  occasionally  the  word  "  ohm  " 
will  leak  out.  Among  these  terms  the  general  reader 
is  apt  to  become  completely  fog-bound.  But  really 
they  are  quite  simple  if  once  understood,  and,  as  we 
shall  see  in  a  moment,  there  are  some  very  remarkable 
instruments  for  measuring  them,  some  of  which  exhibit  a 
delicacy  truly  astonishing. 

It  is  well  at  the  outset  to  try  and  divest  ourselves  of  the 
idea  that  there  is  anything  mysterious  or  occult  about 
electricity.  It  is  quite  true  that  there  are  many  things  about 
it  very  little  understood  even  by  the  most  learned,  but  for 
ordinary  practical  purposes  it  may  be  regarded  as  a  fluid, 
which  flows  along  a  wire  just  as  water  flows  along  a  pipe. 
The  wire  is,  electrically  speaking,  a  "  hole  "  through  the 
air  or  other  non-conducting  substance  with  which  it  is 
surrounded.  A  water-pipe  being  a  hole  through  a  bar  of 

2,2 


MEASURING  ELECTRICITY  28 

iron,  so  the  copper  core  of  an  electrical  wire  is,  so  far  as  the 
current  is  concerned,  but  a  hole  through  the  centre  of  a  tube 
of  silk,  cotton,  rubber  or  whatever  it  be.  Electricity  can 
flow  through  certain  solids  just  as  water  can  flow  through 
empty  space. 

Water  will  not  flow  through  a  pipe  unless  a  pressure  be 
applied  to  it  somewhere.  In  a  pipe  the  ends  of  which  are 
at  the  same  level  water  will  lie  inert  and  motionless.  Lower 
one  end,  however,  and  the  pressure  produced  by  gravity — in 
other  words,  the  weight  of  the  water — -will  cause  it  to  move. 
In  like  manner  pressure  produced  by  the  action  of  a  pump 
will  make  water  flow.  On  the  other  hand,  when  it  moves 
it  encounters  resistance,  through  the  water  rubbing  against 
the  walls  of  the  pipe. 

Similarly,  an  electrical  pressure  is  necessary  before  a 
current  of  electricity  will  flow.  And  every  conductor  offers 
more  or  less  resistance  to  the  flow  of  current,  thus  opposing 
the  action  of  the  pressure.  Before  current  will  flow  through 
your  domestic  glow-lamps  and  cause  them  to  give  light  there 
must  be  a  pressure  at  work,  and  that  pressure  is  described 
as  so  many  volts. 

A  battery  is  really  a  little  automatic  electrical  pump  for 
producing  an  electrical  pressure.  And  the  volt,  which  is  a 
legal  measure,  just  as  much  as  a  pound  or  a  yard,  is  a  certain 
fraction  of  the  pressure  produced  by  a  certain  battery  known 
as  Clark's  Cell.  It  is  not  necessary  here  to  say  exactly  what 
that  fraction  is,  but  it  will  give  a  general  idea  to  state  that 
the  ordinary  Leclanche  or  dry  cell,  such  as  is  used  for  electric 
bells,  produces  a  pressure  of  about  one  and  a  half  volts. 

Thus  we  see  the  volt  is  the  electrical  counterpart  of  the 
term  "  pound  per  square  inch  "  which  is  used  in  the  case  of 
water  pressure. 

A  flow  of  water  is  measured  in  gallons  per  minute.  An 
electrical  current  is  measured  in  coulombs  per  second.  Thus 
the  coulomb  is  the  electrical  counterpart  of  the  gallon. 
But  in  this  particular  we  differ  slightly  in  our  methods  of 
talking  of  water  and  electricity.  Gallons  per  minute  or  per 


24  MEASURING  ELECTRICITY 

hour  is  the  invariable  term  in  the  former  case,  but  in  the 
latter  we  do  not  speak  of  coulombs  per  second,  although 
that  is  what  we  mean,  for  we  have  a  special  name  for  one 
coulomb  per  second,  and  that  same  is  ampere.  One  ampere 
is  one  coulomb  per  second,  two  amperes  are  two  coulombs 
per  second,  and  so  on. 

There  is  no  recognised  term  to  denote  the  resistance  which 
a  water-pipe  offers  to  the  passage  of  water  through  it,  but 
in  the  similar  case  with  electricity  there  is  a  term  specially 
invented  for  the  purpose,  the  ohm.  Legally  it  is  the  resist- 
ance of  a  column  of  mercury  of  a  certain  size  and  weight. 
A  rough  idea  of  it  is  given  by  the  fact  that  a  copper  wire 
a  sixteenth  of  an  inch  thick  and  400  feet  long  has  a 
resistance  of  about  one  ohm. 

The  three  units — the  volt,  ampere  and  ohm — are  so 
related  that  a  pressure  of  one  volt  acting  upon  a  circuit  with 
a  resistance  of  one  ohm  will  produce  a  current  of  one  ampere. 

A  current  can  do  work ;  when  it  lights  or  heats  your  room 
or  drives  a  tramcar  it  is  doing  work  ;  and  the  rate  at  which 
a  current  does  work  is  found  by  multiplying  together  the 
number  of  volts  and  the  number  of  amperes.  The  result 
is  in  still  another  unit,  the  watt.  And  1000  watts  is  a 
kilowatt.  Finally,  to  crown  the  whole  story,  a  kilowatt 
for  one  hour  is  a  Board  of  Trade  unit. 

So  for  every  unit  which  you  pay  for  in  the  quarterly  bill 
you  have  had  a  current  equal  to  1000  watts  for  an  hour. 
To  give  a  concrete  example,  if  the  pressure  of  your  supply 
is  200  volts,  and  you  take  a  current  of  five  amperes  for  an 
hour,  you  will  have  consumed  one  B.T.U. 

Perhaps  it  will  give  added  clearness  to  this  explanation 
to  tabulate  the  terms  as  follow  : — 

Volt  =  The  unit  of  pressure,  analogous  to  "  pounds  per  square 

inch  "  in  the  case  of  water. 

Coulomb  =  The  measure  of  quantity,  analogous  to  the  gallon. 
The  measure  of  the   "strength"   of  a  current, 

meaning  one  coulomb  per  second. 


MEASURING  ELECTRICITY  25 

Watt  =  The  unit  denoting  the  power  for  work  of  any  current. 

It   is   the   result   of   multiplying   together  volts   and 

amperes. 

Kilowatt  =  1000  watts. 
Board  of  Trade  Unit  =  A  current  of  one  kilowatt  flowing  for 

one  hour. 

In  practice  the  measurements  are  generally  made  by 
means  of  the  connection  between  electricity  and  magnetism. 
A  current  of  electricity  is  a  magnet.  Whenever  a  current 
is  flowing  it  is  surrounded  by  a  region  in  which  magnetism 
can  be  felt.  This  region  is  called  the  magnetic  field,  and  the 
strength  of  the  field  varies  with  the  strength  that  is  the 
number  of  amperes  in  the  current.  If  a  wire  carrying  a 
current  be  wound  up  into  a  coil  it  is  evident  that  the  magnetic 
field  will  be  more  intense  than  if  the  wire  be  straight,  for 
it  will  be  concentrated  into  a  smaller  area.  Iron,  with  its 
peculiar  magnetic  properties,  if  placed  in  a  magnetic  field 
seems  to  draw  the  magnetic  forces  towards  itself,  and  con- 
sequently, if  the  wire  be  wound  round  a  core  of  iron,  the 
magnetism  due  to  the  current  will  be  largely  concentrated 
at  the  ends  of  the  core.  But  the  main  principle  remains — 
in  any  given  magnet  the  magnetic  power  exhibited  will  be 
in  proportion  to  the  current  flowing. 

The  switchboard  at  a  generating  station  is  always  supplied 
with  instruments  called  ammeters,  an  abbreviation  of 
amperemeters,  for  the  purpose  of  measuring  the  current 
passing  out  from  the  dynamos.  Each  of  these  consists  of 
a  coil  of  wire  through  which  the  current  passes.  In  some 
there  is  a  piece  of  iron  near  by,  which  is  attracted  more  or 
less  as  the  current  varies,  the  iron  being  pulled  back  by  a 
spring  and  its  movement  against  the  tension  of  the  spring 
being  indicated  by  a  pointer  on  a  dial. 

In  others  the  coil  itself  is  free  to  swing  in  the  neighbour- 
hood of  a  powerful  steel  magnet,  the  interaction  between  the 
electro-magnet,  or  coil,  and  the  permanent  magnet  being 
such  that  they  approach  each  other  or  recede  from  each  other 


26  MEASURING  ELECTRICITY 

as  the  current  varies.     A  pointer  on  a  dial  records  the 
movements  as  before. 

In  yet  another  kind  the  permanent  magnet  gives  way  to 
a  second  coil,  the  current  passing  through  both  in  succession, 
the  result  being  very  much  the  same,  the  two  coils  attracting 
each  other  more  or  less  according  to  the  current. 

Another  kind  of  ammeter  known  as  a  thermo-ammeter 
works  on  quite  a  different  principle.  It  consists  of  a  piece 
of  fine  platinum  wire  which  is  arranged  as  a  "  shunt " — that 
is  to  say,  a  certain  small  but  definite  proportion  of  the 
current  to  be  measured  passes  through  it.  Now,  being  fine, 
the  current  has  considerable  difficulty  in  forcing  its  way 
through  this  wire  and  the  energy  so  expended  becomes 
turned  into  heat  in  the  wire.  It  is  indeed  a  mild  form  of 
what  we  see  in  the  filament  of  an  incandescent  lamp,  where 
the  energy  expended  in  forcing  the  current  through  makes 
the  filament  white-hot.  The  same  principle  is  at  work 
when  we  rub  out  a  pencil  mark  with  india-rubber,  whereby 
the  rubber  becomes  heated,  as  most  of  us  have  observed. 
The  wire,  then,  is  heated  by  the  current  passing  through  it, 
and  accordingly  expands,  the  amount  of  expansion  forming  J 
an  indication  of  the  current  passing.  The  elongation  of  the 
wire  is  made  to  turn  a  pointer. 

A  simple  modification  makes  any  of  these  instruments 
into  a  voltmeter.  This  instrument  is  intended  to  measure 
the  force  or  pressure  in  the  current  as  it  leaves  the  dynamo. 

A  short  branch  circuit  is  constructed,  leading  from  the 
positive  wire  near  the  dynamo  to  the  negative  wire,  or  to 
the  earth,  where  the  pressure  is  zero.  In  this  circuit  is 
placed  the  instrument,  together  with  a  coil  made  of  a  very 
long  length  of  fine  wire  so  that  it  has  a  very  great  resistance. 
Very  little  current  will  flow  through  the  branch  circuit 
because  of  the  high  resistance  of  the  coil,  but  what  there  is 
will  be  in  exact  proportion  to  the  pressure.  The  voltmeter 
is  therefore  the  same  as  the  ammeter,  except  that  its  dial  is 
marked  for  volts  instead  of  for  amperes,  and  it  has  to  be 
provided  with  the  resistance  coil. 


MEASURING  ELECTRICITY  27 

Instruments  of  the  ammeter  type  can  also  be  used  as 
ohmmeters.  In  this  case  what  is  wanted  is  to  test  the 
resistance  of  a  circuit,  and  it  is  done  by  applying  a  battery, 
the  voltage  of  which  is  known,  and  seeing  how  much  current 
flows. 

All  the  voltmeters  and  ohmmeters  mentioned  owe  their 
method  of  working  to  what  is  known  as  Ohm's  law.  One 
of  the  greatest  steps  in  the  development  of  electrical  science 
was  taken  when  Dr  Ohm  put  forward  the  law  which  he 
had  discovered  whereby  pressure,  current  and  resistance  are 
related.  The  reader  will  probably  have  noticed  from  what 
has  already  been  said  about  the  units  of  measurement — 
the  volt,  the  ampere  and  the  ohm — that  the  current  varies 
directly  as  the  pressure  and  inversely  as  the  resistance. 
That  is  the  famous  and  important 4t  Ohm's  law  "  and  anyone 
who  has  once  grasped  that  has  gone  a  long  way  towards 
understanding  many  of  the  principal  phenomena  of  electric 
currents. 

But  the  instruments  so  far  referred  to  are  of  the  big, 
clumsy  type,  suitable  for  measuring  large  currents  and  great 
pressures.  They  are  like  the  great  railway  weigh-bridges, 
which  weigh  a  whole  truck-load  at  a  time  and  are  good 
enough  if  they  are  true  to  a  quarter  of  a  hundredweight. 
The  instruments  about  to  be  described  are  more  comparable 
with  the  delicate  balance  of  the  chemist,  which  can  detect 
the  added  weight  when  a  pencil  mark  is  made  upon  a  piece 
of  paper.  Indeed  beside  them  such  a  balance  is  quite  crude 
and  clumsy.  They  may  be  said  to  be  the  most  delicate 
measuring  instruments  in  existence. 

We  will  commence  with  the  galvanometer.  The  simplest 
form  of  this  is  a  needle  like  that  of  a  mariner's  compass 
very  delicately  suspended  by  a  thin  fibre  in  the  neighbour- 
hood of  a  coil  of  wire.  The  magnetic  field  produced  by  the 
current  flowing  in  the  wire  tends  to  turn  the  needle,  which 
movement  is  resisted  by  its  natural  tendency  to  point 
north  and  south.  Thus  the  current  only  turns  the  needle 
a  certain  distance,  which  distance  will  be  in  proportion  to 


28  MEASURING  ELECTRICITY 

its  strength.    The  deflection  of  the  needle,  therefore,  gives 
us  a  measure  of  the  strength  of  the  current. 

But  such  an  instrument  is  not  delicate  enough  for  the  most 
refined  experiments,  and  the  improved  form  generally  used 
is  due  to  that  prince  of  inventors,  the  late  Lord  Kelvin. 
He  originally  devised  it,  it  is  interesting  to  note,  not  for 
laboratory  experiments,  but  for  practical  use  as  a  telegraph 
instrument  in  connection  with  the  early  Atlantic  cables. 

Before  describing  it,  it  may  sharpen  the  reader's  interest 
to  mention  a  wonderful  experiment  which  was  made  by 
Varley,  the  famous  electrician,  on  the  first  successful  Atlantic 
cable.  He  formed  a  minute  battery  of  a  brass  gun -cap, 
with  a  scrap  of  zinc  and  a  single  drop  of  acidulated  water. 
This  he  connected  up  to  the  cable.  Probably  there  is  not 
one  reader  of  this  book  but  would  have  thought,  if  he  had 
been  present,  that  the  man  was  mad.  What  conceivable 
good  could  come  of  connecting  such  a  feeble  source  of 
electrical  pressure  to  the  two  thousand  miles  of  wire  spanning 
the  great  ocean ;  the  very  idea  seems  fantastic  in  the 
extreme.  Yet  that  tiny  battery  was  able  to  make  its  power 
felt  even  over  that  great  distance,  for  the  Thomson  Mirror 
Galvanometer  was  there  to  detect  it.  Two  thousand  miles 
away,  the  galvanometer  felt  and  was  operated  by  the  force 
generated  in  a  battery  about  the  size  of  one  of  the  capital 
letters  on  this  page. 

This  wonderful  instrument  consisted  of  a  magnet  made  of 
a  small  fragment  of  watch-spring,  suspended  in  a  horizontal 
position  by  means  of  a  thread  of  fine  silk,  close  to  a  coil  of 
fine  wire.  When  current  flowed  through  the  coil  the  magnetic 
field  caused  the  watch-spring  magnet  to  swing  round,  but 
when  the  current  ceased  the  untwisting  of  the  silk  brought 
it  back  to  its  original  position  again. 

So  far  it  seems  to  differ  very  little  from  the  ordinary  gal- 
vanometer previously  mentioned,  but  the  stroke  of  genius 
was  in  the  method  of  reading  it.  With  a  small  current  the 
movement  of  the  magnet  was  too  small  to  be  observed  by 
the  unaided  eye,  so  it  was  attached  to  a  minute  mirror 


MEASURING  ELECTRICITY  29 

made  of  one  of  those  little  circles  of  glass  used  for  covering 
microscope  slides,  silvered  on  the  back.  The  magnet  was 
cemented  to  the  back  of  this,  yet  both  were  so  small  that 
together  their  weight  was  supported  by  a  single  thread  of 
cocoon  silk.  Light  from  a  lamp  was  made  to  fall  upon  this 
mirror,  thereby  throwing  a  spot  of  light  upon  a  distant  screen. 
Thus  the  slightest  movement  of  the  magnet  was  magnified 
into  a  considerable  movement  of  the  spot  of  light.  The  beam 
of  light  from  the  mirror  to  the  screen  became,  in  fact,  a 
long  lever  or  pointer,  without  weight  and  without  friction. 

The  task  of  watching  the  rocking  to  and  fro  of  the  spot  of 
light  was  found  to  be  too  nerve-racking  for  the  telegraph 
operators,  and  so  Lord  Kelvin  improved  upon  his  galvano- 
meter in  two  ways.  He  first  of  all  managed  to  give  it 
greater  turning-power,  so  that,  actuated  by  the  same  current, 
the  new  instrument  would  work  much  more  strongly  than 
the  older  one.  Then  he  utilised  this  added  power  to  move 
a  pen  whereby  the  signals  were  recorded  automatically 
upon  a  piece  of  paper.  The  new  instrument  is  known  as 
the  Siphon  Recorider. 

The  added  power  was  obtained  by  turning  the  instrument 
inside  out,  as  it  were,  making  the  coil  the  moving  part  and 
the  permanent  magnet  the  fixed  part.  This  enabled  him 
to  employ  a  very  powerful  permanent  magnet  in  place  of 
the  minute  one  made  of  watch-spring.  The  interaction  of 
two  magnets  is  the  result  of  their  combined  strength,  and 
that  of  the  coil  being  limited  by  the  strength  of  the  minute 
current  the  only  way  to  increase  the  combined  power  of  the 
two  was  to  substitute  a  large  powerful  magnet  for  the  small 
magnetised  watch-spring.  This  large  magnet  would,  of 
course,  have  been  too  heavy  to  swing  easily  and  therefore 
the  positions  had  to  be  reversed. 

So  now  we  have  two  types  of  galvanometer,  both  due  origin- 
ally to  the  inventions  of  Lord  Kelvin.  For  some  purposes 
the  Thomson  type  (his  name  was  Thomson  before  he  became 
Lord  Kelvin)  are  still  used,  but  in  a  slightly  elaborated  form. 
Its  sensitiveness  is  such  that  a  current  of  a  thousandth  of 


80  MEASURING  ELECTRICITY 

a  micro-ampere  will  move  the  spot  of  light  appreciably. 
And  when  one  comes  to  consider  that  a  micro-ampere  is  a 
millionth  part  of  an  ampere  this  is  perfectly  astounding. 

But  there  is  a  more  wonderful  story  still  to  come,  of  an 
instrument  which  can  detect  a  millionth  of  a  micro-ampere, 
r  _  or  one  millionth  of  a  millionth  of 

an  ampere.  It  is  not  generally 
known  that  we  are  all  possessors 
of  an  electric  generator  in  the 
form  of  the  human  heart,  but  it 
is  so,  and  Professor  Einthoven,  of 
Leyden,  wishing  to  investigate  these 
currents  from  the  heart,  found  him- 
self in  need  of  a  galvanometer  ex- 
ceeding in  sensitiveness  anything  then 
known.  Even  the  tiny  needles  or 
coils  with  their  minute  mirrors  have 
some  weight  and  so  possess  in  an 
&  appreciable  degree  the  property  of 
inertia,  in  virtue  of  which  they  are 
Q~  **  loath  to  start  movement  and,  having 

FIG.  i.—  This  stows  the  prm-  started,  are  reluctant  to  stop.    This 

ciple  of  this  wonderful  Galvano  .....  ,      .  -T. 

meter  invented  by  Lord  Kelvin  inertia,  it  IS  eaSV  to  See,  militates 
in  its  latest  form.  Current  enters  ,  ,  ,  .  „ 

at  a,  passes  round  the  coils,  as  against   the    accurate   recording    of 

shown  by  the  arrows,  and  away  .  1  •    ,  • 

at  6.  A  light  rod,  c,  is  suspended  rapid  variations  in  minute  currents, 

by  the  fine  fibre,  d,  so  that  the         *    t  .-      T»      j?  i 

eight  little  magnets  hang  in  the  SO  the  energetic   ProfeSSOr    Set   about 

centres  of  the  coils—  four  in  each.  ,       .    .  ,  .  .    . 

The  current  deflects  these  magnets  deVlSUlg    a    nCW    galvanometer   which 


and  so  turns  the  mirror,  m,  at  the  ,         ••  j  ,  .  mi  . 

bottom  of  the  rod.  At  e  are  two  should   answer    his    purpose.      This 

large  magnets  which  give  the  little  ,  .,         tt  o,    • 

ones   the  necessary  tendency  to  IS    knOWn    aS    the         String 


meter." 

The  main  body  of  the  instrument  is  a  large,  powerful 
electro-magnet,  in  shape  like  a  large  pair  of  jaws  nearly  shut. 
Energised  by  a  strong  current,  this  magnet  produces  an  ex- 
ceedingly strong  magnetic  field  in  the  small  space  between 
the  "  teeth  "  as  it  were.  In  this  space  there  is  stretched  a 
fine  thread  of  quartz  which  is  almost  perfectly  elastic.  It 
is  a  non-conductor,  however,  so  it  is  covered  with  a  fine 


MEASURING  ELECTRICITY 


31 


coating  of  silver.  Silver  wire  is  sometimes  used,  but  no 
way  has  yet  been  found  of  drawing  any  metallic  wire  so 
thin  as  the  quartz  fibre,  which  is  sometimes  as  thin  as  two 
thousandths  of  a  millimetre,  or  about  a  twelve-thousandth 
of  an  inch.  A  hundred  pages  of  this  book  make  up  a  thick- 
ness of  about  an  inch,  so  that  one  leaf  is  about  a  fiftieth 
of  an  inch.  Consequently  the  fibre  in  question  could  be 
multiplied  240  times  before  it 
became  as  stout  as  the  paper 
on  which  these  words  are  printed. 
The  current  to  be  measured, 
then,  is  passed  through  the 
stretched  fibre  and  the  interaction 
of  the  magnetic  field  by  which 
the  fibre  is  then  surrounded,  with 
the  magnetic  field  in  which  it  is 
immersed,  causes  it  to  be  deflected 
to  one  side.  Of  course  the  de- 
flection is  exceedingly  small  in 
amount,  and  as  it  is  undesirable 

tn    TiamriP^  ifc   mrrtr*vmonf «  Vrvr  tl>^ 

ro  namper  its  movements  oy  tne 

weight    of  a   mirror,  no  matter 

how  small,  some  other  means  of 

reading  the  instrument  had  to  be  bends  more  or  less- 

devised.    This  is  a  microscope  which  is  fixed  to  one  of  the 

jaws,  through  a  fine  hole  in  which  the  movements  of  the 

fibre  can  be  viewed.    Or  what  is  often  better  still,  a  picture 

of  the  wire  can  be  projected  through  the  microscope  on  to 

a  screen  or  on  to  a  moving  photographic  plate  or  strip  of 

photographic  paper.    In  the  latter  case  a  permanent  record 

is  made  of  the  changes  in  the  flowing  current. 

An  electric  picture  can  thus  be  made  of  the  working  of  a 
man's  heart.  He  holds  in  his  hands  two  metal  handles 
or  is  in  some  other  way  connected  to  the  two  ends  of  the 
fibre  by  wires  just  as  the  handles  of  a  shocking  coil  are  con- 
nected to  the  ends  of  the  coil.  The  faint  currents  caused 
by  the  beating  of  his  heart  are  thus  set  down  in  the  form  of 


PIG.  2.— Here  we  see  the  working 
parts  of  the  "String  Galvanometer," 
by  which  the  beating  of  the  heart 


32  MEASURING  ELECTRICITY 

a  wavy  line.  Such  a  diagram  is  called  a  "  cardiogram,"  and 
it  seems  that  each  of  us  has  a  particular  form  of  cardiogram 
peculiar  to  himself,  so  that  a  man  could  almost  be  recognised 
and  distinguished  from  his  fellows  by  the  electrical  action 
of  his  heart. 

The  galvanometer  has  a  near  relative,  the  electrometer, 
the  astounding  delicacy  of  which  renders  it  equally  interest- 
ing. It  is  particularly  valuable  in  certain  important  in- 
vestigations as  to  the  nature  and  construction  of  atoms. 

The  galvanometer,  it  will  be  remembered,  measures  minute 
currents;  the  electrometer  measures  minute  pressures, 
particularly  those  of  small  electrically  charged  bodies. 

Every  conductor  (and  all  things  are  conductors,  more  or 
less)  can  be  given  a  charge  of  electricity.  Any  insulated  wire, 
for  example,  if  connected  to  a  battery  will  become  charged 
— current  will  flow  into  it  and  there  remain  stationary.  And 
that  is  what  we  mean  by  a  charge  as  opposed  to  a  current. 

Air  compressed  into  a  closed  vessel  is  a  charge.  Air, 
however  compressed,  flowing  along  a  pipe  would  be  better 
described  as  a  current. 

Imagine  one  of  those  cylinders  used  for  the  conveyance 
of  gas  under  pressure  and  suppose  that  we  desire  to  find 
the  pressure  of  the  gas  with  which  it  is  charged.  We  connect 
a  pressure-gauge  to  it,  and  see  what  the  finger  of  the  gauge 
has  to  say.  What  happens  is  that  gas  from  the  cylinder 
flows  into  the  little  vessel  which  constitutes  the  gauge  and 
there  records  its  own  pressure. 

And  just  the  same  applies  with  electrometers.  Precisely 
as  the  pressure-gauge  measures  the  pressure  of  air  or  gas 
in  some  vessel,  so  the  electrometer  measures  the  electrical 
pressure  in  a  charged  body. 

Further,  some  of  the  charged  bodies  with  which  the 
student  of  physics  is  much  concerned  are  far  smaller  than 
can  be  seen  with  the  most  powerful  microscope.  How 
wonderfully  minute  and  delicate,  therefore,  must  be  the 
instrument  which  can  be  influenced  by  the  tiny  charge 
which  so  small  a  body  can  carry. 


MEASURING  ELECTRICITY  33 

It  will  be  interesting  here  to  describe  an  experiment 
performed  with  an  electrometer  by  Professor  Rutherford, 
by  which  he  determined  how  many  molecules  there  are  in 
a  centimetre  of  gas,  a  number  very  important  to  know  but 
very  difficult  to  ascertain,  since  molecules  are  too  small 
to  be  seen.  This  number,  by  the  way,  is  known  to  science 
as  "  Avogadro's  Constant." 

Everyone  has  heard  of  radium,  and  knows  that  it  is  in 
a  state  which  can  best  be  described  as  a  long-drawn-out 
explosion.  It  is  always  shooting  off  tiny  particles.  Night 
and  day,  year  in  and  year  out,  it  is  firing  off  these  exceedingly 
minute  projectiles,  of  which  there  are  two  kinds,  one  of 
which  appears  to  be  atoms  of  helium. 

Some  years  ago,  when  radium  was  being  much  talked  about 
and  thena  mes  of  M.  and  Madame  Curie  were  in  everyone's 
mouth,  little  toys  were  sold,  the  invention,  I  believe,  of 
Sir  William  Crookes,  called  spinthariscopes.  Each  of  these 
consisted  of  a  short  brass  tube  with  a  small  lens  in  one  end. 
Looking  through  the  lens  in  a  dark  room,  one  could  see 
little  splashes  of  light  on  the  walls  of  the  tube.  Those 
splashes  were  caused  by  a  tiny  speck  of  radium  in  the  middle 
of  the  tube,  the  helium  atoms  from  which,  by  bombarding 
the  inner  surface  of  the  tube,  produced  the  sparks. 

Now  if  we  can  count  those  splashes  we  can  tell  how  many 
atoms  of  helium  are  being  given  off  per  minute.  And  if 
then  we  reckon  how  many  minutes  it  takes  to  accumulate 
a  cubic  centimetre  of  helium  we  can  easily  reckon  how 
many  atoms  go  to  the  cubic  centimetre.  But  the  difficulty 
is  to  count  them. 

So  the  learned  Professor  called  in  the  aid  of  the  electro- 
meter. He  could  not  count  all  the  atoms  shot  off,  so  he 
put  the  piece  of  radium  at  one  end  of  a  tube  and  an  electro- 
meter at  the  other.  Every  now  and  then  an  atom  shot 
right  through  the  tube  and  out  at  the  farther  end.  And 
since  each  of  these  atoms  from  radium  is  charged  with 
electricity,  each  as  it  emerged  operated  the  electrometer. 
By  simply  watching  the  twitching  of  the  instrument, 
c 


34  MEASURING  ELECTRICITY 

therefore,  it  was  possible  to  count  how  many  atoms  shot 
through  the  tube — one  atom  one  twitch.  And  from  the  size 
and  position  of  the  tube  it  was  possible  to  reckon  what 
proportion  of  the  whole  number  shot  off  would  pass  that  way . 

The  result  of  the  experiment  showed  that  there  are  in  a 
cubic  centimetre  of  helium  a  number  of  atoms  represented 
by  256  followed  by  seventeen  noughts.  And  as  helium  is 
one  of  the  few  substances  in  which  the  molecule  is  formed  of 
but  one  atom,  that  is  also  the  number  of  molecules. 

And  now  consider  this,  please.  A  cubic  centimetre  is 
about  the  size  of  a  boy's  marble.  That  contains  the  vast 
number  of  molecules  just  mentioned.  And  the  electrometer 
was  able  to  detect  the  presence  of  those  one  at  a  time.  Need 
one  add  another  word  as  to  the  inconceivable  delicacy  of 
the  instrument. 

In  its  simplest  form  the  electrometer  is  called  the  "  electro- 
scope." Two  strips  of  gold-leaf  are  suspended  by  their 
ends  under  a  glass  or  metal  shade.  As  they  hang  normally 
they  are  in  close  proximity.  Their  upper  ends  are,  in  fact, 
in  contact  and  are  attached  to  a  small  vertical  conductor. 
A  charge  imparted  to  the  small  conductor  will  pass  down 
into  the  leaves,  and  since  it  will  charge  them  both  they 
will  repel  each  other  so  that  their  lower  ends  will  swing 
apart.  Such  an  instrument  is  very  delicate,  but  because 
of  the  extreme  thinness  of  the  leaves  it  is  very  diffi- 
cult to  read  accurately  the  amount  of  their  movement  and 
so  to  determine  the  charge  which  has  been  given  to  them. 

In  a  more  recent  improvement,  therefore,  only  one  strip 
of  gold-leaf  is  used,  the  place  of  the  other  being  taken  by  a 
copper  strip.  The  whole  of  the  movement  is  thus  in  the 
single  gold-leaf,  as  the  copper  strip  is  comparatively  stiff, 
and  it  is  possible  to  arrange  for  the  movement  of  this  one 
piece  of  gold-leaf  to  be  measured  by  a  microscope. 

The  other  principal  kind  of  electrometer  we  owe,  as  we 
do  the  galvanometers,  to  the  wonderful  ingenuity  of  Lord 
Kelvin.  In  this  the  moving  part  is  a  strip  of  thin  aluminium, 
which  is  suspended  in  a  horizontal  position  by  means, 


MEASURING  ELECTRICITY  35 

generally,  of  a  fine  quartz  fibre.  Since  it  is  necessary  that  this 
fibre  should  be  a  conductor,  which  quartz  is  not,  it  is  electro- 
plated with  silver.  Thus  a  charge  communicated  to  the 
upper  end  of  the  fibre,  where  it  is  attached  to  the  case, 
passes  down  to  the  aluminium  "needle,"  as  it  is  called. 
Now  the  needle  is  free  to  swing  to  and  fro,  with  a  rotating 
motion,  between  two  metal  plates  carefully  insulated. 
Each  plate  is  cut  into  four  quadrants,  the  opposite  ones  being 
electrically  connected,  while  all  are  insulated  from  their 
nearest  neighbours.  One  set  of  quadrants  is  charged  posi- 
tively, and  one  set  negatively,  by  a  battery,  but  these 
charges  have  no  effect  upon  the  needle  until  it  is  itself 
charged.  As  soon  as  that  occurs,  however,  they  pull  it 
round,  and  the  amount  of  its  movement  indicates  the  amount 
of  the  charge  upon  the  needle,  and  therefore  the  pressure 
existing  upon  the  charged  body  to  which  it  is  connected. 
The  direction  of  its  movement  shows,  moreover,  whether 
the  charge  be  positive  or  negative. 

A  little  mirror  is  attached  to  the  needle,  so  that  its  slightest 
motion  is  revealed  by  the  movement  of  a  spot  of  light,  as 
in  the  case  of  the  mirror  galvanometers.  Instruments  such 
as  these  are  called  "  Quadrant  Electrometers." 

My  readers  will  remember,  too,  the  "  String  Galvanometer  " 
already  mentioned.  The  same  idea  has  been  adapted  to 
this  purpose.  A  fine  fibre  is  stretched  between  two  charged 
conductors  while  the  fibre  is  itself  connected  to  the  body 
whose  charge  is  being  measured.  The  charge  which  it 
derives  from  the  body  causes  it  to  be  deflected,  which 
deflection  is  measured  by  a  microscope. 

In  all  cases  of  transmission  of  electricity  over  long  distances 
for  lighting  or  power  purposes  the  currents  are  "  alter- 
nating." They  flow  first  one  way  and  then  the  other, 
reversing  perhaps  twenty  times  a  second,  or  it  may  be  two 
hundred,  or  even  more  times  in  that  short  period.  Some 
electric  railways  are  worked  with  alternating  current,  and 
it  is  used  for  lighting  quite  as  much  as  direct  current  and 
is  equally  satisfactory. 


36  MEASURING  ELECTRICITY 

In  wireless  telegraphy  it  is  essential.  In  that  case, 
however,  the  reversals  may  take  place  millions  of  times  per 
second.  Consequently,  to  distinguish  the  comparatively 
slowly  changing  currents  of  a  "  frequency  "  or  "  periodicity  " 
of  a  few  hundreds  per  second  from  these  much  more  rapid 
ones,  the  latter  are  more  often  spoken  of  as  electrical  oscilla- 
tions. And  these  alternating  and  oscillating  currents  need 
to  be  measured  just  as  the  direct  currents  do.  Yet  in  many 
cases  the  same  instruments  will  not  answer.  There  has 
therefore  grown  up  a  class  of  wonderful  measuring  instru- 
ments specially  designed  for  this  purpose,  by  which  not  only 
does  the  station  engineer  know  what  his  alternating  current 
dynamos  are  doing,  but  the  wireless  operator  can  tell  what 
is  happening  in  his  apparatus,  the  investigator  can  probe 
the  subtleties  of  the  currents  which  he  is  wrorking  with,  and 
apparatus  for  all  purposes  can  be  designed  and  worked  with 
a  system  and  reason  which  would  be  impossible  but  for  the 
possibility  of  being  able  to  measure  the  behaviour  of  the 
subtle  current  under  all  conditions. 

One  trouble  in  connection  with  measuring  these  alternating 
currents  is  that  they  are  very  reluctant  to  pass  through  a 
coil. 

One  method  by  which  this  difficulty  can  be  overcome  has 
been  mentioned  incidentally  already.  I  refer  to  the  heating 
of  a  wire  through  which  current  is  passing.  This  is  just 
the  same  whether  the  current  be  alternating  or  direct. 

One  of  the  simplest  instruments  of  this  class  has  been 
appropriated  by  the  Germans,  who  have  named  it  the  "  Reiss 
Electrical  Thermometer,"  although  it  was  really  invented 
nearly  a  century  ago  by  Sir  William  Snow  Harris.  It 
consists  of  a  glass  bulb  on  one  end  of  a  glass  tube.  The 
current  is  passed  through  a  fine  wire  inside  this  bulb,  and 
as  the  wire  becomes  heated  it  expands  the  air  inside  the 
bulb.  This  expansion  moves  a  little  globule  of  mercury 
which  lies  in  the  tube,  and  which  forms  the  pointer  or 
indicator  by  which  the  instrument  is  read.  As  the  tempera- 
ture of  the  wire  rises  the  mercury  is  forced  away  from  the 


MEASURING  ELECTRICITY  37 

bulb,  as  the  temperature  falls  it  returns.  And  as  the 
temperature  is  varied  by  the  passage  of  the  current,  so  the 
movement  of  the  mercury  is  a  measure  of  the  current. 

Another  way  is  to  employ  a  "  Rectifier."  This  is  a  con- 
ductor which  has  the  peculiar  property  of  allowing  current 
to  pass  one  way  but  not  the  other.  It  thus  eliminates  every 
alternate  current  and  changes  the  alternating  current  into 
a  series  of  intermittent  currents  all  in  the  same  direction. 
Rectified  current  is  thus  hardly  described  by  the  term  con- 
tinuous, but  still  it  is  "  continuous  current "  in  the  sense 
that  the  flow  is  always  in  the  same  direction,  and  so  it  can 
be  measured  by  the  ordinary  continuous  current  instruments. 
The  difficulty  about  it  is  that  there  is  some  doubt  as  to  the 
relation  between  the  quantity  of  rectified  current  which  the 
galvanometer  registers  and  the  quantity  of  alternating 
current,  which  after  all  is  the  quantity  which  is  really  to 
be  measured.  How  the  rectification  is  accomplished  will  be 
referred  to  again  in  the  chapter  on  Wireless  Telegraphy. 

But  to  return  to  the  thermo-galvanometers,  as  those  are 
termed  which  ascertain  the  strength  of  a  current  by  the 
heat  which  it  produces,  the  simple  little  contrivance  of 
Sir  William  Snow  Harris  has  more  elaborate  successors, 
of  which  perhaps  the  most  interesting  are  those  associated 
with  the  name  of  Mr  W.  Duddell,  who  has  made  the  sub- 
ject largely  his  own.  Besides  their  interest  as  wonderfully 
delicate  measuring  instruments,  these  have  an  added  interest, 
since  they  introduce  us  to  another  strange  phenomenon  in 
electricity.  We  have  just  noted  the  fact  that  electricity 
causes  heat.  Now  we  shall  see  the  exact  opposite,  in  which 
heat  produces  electrical  pressure  and  current.  And  the 
feature  of  Mr  DuddelPs  instruments  is  the  way  in  which 
these  two  things  are  combined.  By  a  roundabout  but  very 
effective  way  he  rectifies  the  current  to  be  measured,  for 
he  first  converts  some  of  the  alternating  current  into  heat 
and  then  converts  that  heat  into  continuous  current. 

If  two  pieces  of  dissimilar  metals  be  connected  together 
by  their  ends,  so  as  to  form  a  circuit,  and  one  of  the  joints  be 


38  MEASURING  ELECTRICITY 

heated,  an  electrical  pressure  will  be  generated  which  will 
cause  a  current  to  flow  round  the  circuit.  The  direction  in 
which  it  will  flow  will  depend  upon  the  metals  employed. 
The  amount  of  the  pressure  will  also  depend  upon  the  metals 
used,  combined  with  the  temperature  of  the  junctions.  With 
any  given  pair  of  metals,  however,  the  force,  and  therefore 
the  volume  of  current,  will  vary  as  the  temperature.  Really 
it  will  be  the  difference  in  temperature  between  the  hot 
junction  and  the  cold  junction,  but  if  we  so  arrange  things 
that  the  cold  junction  shall  always  remain  about  the  same, 
the  current  which  flows  will  vary  as  the  temperature  of  the 
hot  one.  The  volume  of  that  current  will  therefore  be  a 
measure  of  the  temperature.  Such  an  arrangement  is 
known  as  a  thermo-couple,  and  is  becoming  of  great  use 
in  many  manufacturing  processes  as  a  means  of  measuring 
temperatures. 

In  the  Duddell  Thermo-galvanometers,  therefore,  the 
alternating  current  is  first  led  to  a  "  heater  "  consisting  of 
fine  platinised  quartz  fibre  or  thin  metal  wires.  Just  above 
the  heater  there  hangs  a  thermo-couple,  consisting  of  two 
little  bars,  one  of  bismuth  and  the  other  of  antimony.  These 
two  are  connected  together  at  their  lower  end,  where  they 
nearly  touch  the  heater,  but  their  upper  ends  are  kept  a 
little  apart,  being  joined,  however,  by  a  loop  formed  of 
silver  strip.  This  arrangement  will  be  quite  clear  from  the 
accompanying  sketch,  and  it  will  be  observed  that  the  loop 
is  so  shaped  that  the  whole  thing  can  be  easily  suspended 
by  a  delicate  fibre  which  will  permit  it  to  swing  easily, 
like  the  coil  in  a  mirror  galvanometer. 

It  is  indeed  a  swinging  coil  of  a  galvanometer  formed 
with  a  single  turn  instead  of  the  many  turns  usual  in  the 
ordinary  instruments,  and  it  will  be  noticed  from  the  sketch 
that  there  is  a  mirror  fixed  just  above  the  top  of  the  loop. 

This  coil,  then,  with  the  thermo-couple  at  its  lower 
extremity,  is  hung  between  the  ends  of  a  powerful  magnet 
much  as  the  fibre  of  the  Einthoven  Galvanometer  is 
situated.  The  alternating  current  to  be  measured  comes 


MEASURING  ELECTRICITY 


39 


along  through  the  heater.  The  heater  rises  in  temperature. 
That  warms  the  lower  end  of  the  thermo-couple.  Instantly 
a  steady,  continuous  current  begins  to  circulate  round  the 
silver  strip  which  forms  the  coil,  and  that,  acting  just  as  the 
current  does  in  the  ordinary  galvanometer,  causes  the  coil  to 
swing  round  more  or  less,  which  movement  is  indicated  by 
the  spot  of  light  from  the 
mirror.  A  current  as  small 
as  twenty  micro-amperes  (or 
twenty  millionths  of  an  am- 
pere) can  be  measured  in  this 
way. 

Mr  Duddell  has  also  per- 
fected a  wonderful  instrument 
called  an  Oscillograph,  for  the 
strange  purpose  of  making 
actual  pictures  of  the  rise  and 
fall  in  volume  of  current  in 
alternating  circuits. 

To  realise  the  almost   mi- 
raculous   delicacy    of    these 
wonderful     instruments     we    ft  -* -"-» ••*- 
need  first  of  all  to  construct     FlG-  3-~The 


DuSlr"  Therm°-galvan°- 

a  mpntal  r»iptnvp  nf  wh«t  fpVp<l        In  this  remarkable  instrument  alternating 

a  mental  picture  01  wnat  taKes  current  enters  at  0>  paS3es  through  the  fine 

r»iTYvmf      fhrnnwli     wire  and  leaves  at  6.     In  doing  this  it  heats 

circuit    tnrougn  the  wirej  which  in  turn  h  ts  the  lower  end 

of  the  bismuth  and  antimony  bars.      This 


through  the  loop  of  silver  wire,  c,  which,  since 

.t  ha  «gg  betwe^n  the  poles>  d-  and  gj  of  a 

magnet,  is  thereby  turned  more  or  less.    The 

am*unt'of  the  tu/ning  indicates  the  strength 

of  the  alternating  current. 


lflPP       n      fl 

piace    in    a 

wTiiph     fllfpTnatino1     Piirrpnt      <5 

wmcn   alternating  current  i* 

rm  Q«iin  Cf        TfiP    r»nvrpr»t    llPO-in<i 

passing.  rrent  oegins 

to  fln\V  •     it  o-VPflnflllv  inf»fPP<JP«J 

)  now  .  it  graauaiiy  increases 

in  VOlume   Until    it   reaches   itS 

maximum  :  then  it  begins  to  die  away  until  it  becomes 
nil  :  then  it  begins  to  grow  in  the  opposite  direction, 
increases  to  its  maximum  and  dies  away  once  more.  That 
cycle  of  events  occurs  over  and  over  again  at  the  rate 
it  may  be  of  hundreds  of  times  per  second.  Now  for 
the  actual  efficient  operation  of  electrical  machinery 
working  on  alternating  current  it  is  very  necessary  to 
know  exactly  how  those  changes  take  place  —  do  they 


40  MEASURING  ELECTRICITY 

occur  gradually,  the  current  growing  and  increasing  in 
volume  regularly  and  steadily,  or  irregularly  in  a  jumpy 
manner  ?  Engineers  have  a  great  fancy  for  setting  out 
such  changes  in  the  form  of  diagrams,  in  which  case  the 
alternations  are  represented  by  a  wavy  line,  and  it  is 
of  much  importance  to  obtain  an  actual  diagram  showing 
not  what  the  changes  should  be  according  to  theory,  but 
what  they  really  are  in  practice.  It  is  then  possible  to 
see  whether  the  "  wave-form "  of  the  current  is  what  it 
ought  to  be. 

Once  again  we  must  turn  our  thoughts  back  to  the  string 
galvanometer.  In  that  case,  it  will  be  remembered,  there 
is  a  conducting  fibre  passing  between  the  ends  or  poles 
of  a  powerful  magnet,  the  result  of  which  arrangement 
is  that  as  the  current  passes  through  the  fibre  it  is  bent 
by  the  action  of  the  magnetic  forces  produced  around  it. 
If  the  current  pass  one  way,  downwards  let  us  say,  the 
fibre  will  be  bent  one  way,  while  if  it  pass  upwards  it  will 
be  bent  the  opposite  way.  Suppose  then  that  we  have 
two  fibres  instead  of  one,  and  that  we  send  the  current  up 
one  and  down  the  other.  One  will  be  bent  inwards  and 
the  other  outwards.  Then  suppose  that  we  fix  a  little 
mirror  to  the  centre  of  the  fibres,  one  side  of  it  being 
attached  to  one  fibre  and  the  other  to  the  other.  As  one 
fibre  advances  and  the  other  recedes  the  mirror  will  be 
turned  more  or  less.  Consequently,  as  the  current  flowing 
in  the  fibres  increases  or  decreases,  or  changes  in  direction, 
the  mirror  will  be  slewed  round  more  or  less  in  one  direction 
or  the  other. 

The  spot  of  light  thrown  by  the  mirror  will  then  dance 
from  side  to  side  with  every  variation,  and  if  it  be  made  to 
fall  upon  a  rapidly  moving  strip  of  photograph  paper  a 
wavy  line  will  be  drawn  upon  the  paper  which  will  faithfully 
represent  the  changes  in  the  current. 

In  its  action,  of  course,  it  is  not  unlike  an  ordinary 
mirror  galvanometer,  but  its  special  feature  is  in  the 
mechanical  arrangement  of  its  parts  which  enable  it  to 


MEASURING  ELECTRICITY  41 

move  with  sufficient  rapidity  to  follow  the  rapidly  succeed- 
ing changes  which  need  to  be  investigated.  It  is  far  less 
sensitive  than,  say,  a  Thomson  Galvanometer,  but  the 
latter  could  not  respond  quickly  enough  for  this  particular 
purpose. 


CHAPTER  III 

THE  FUEL  OF  THE   FUTURE 

WE  now  enter  for  a  while  the  realm  of  organic 
chemistry,  a  branch  of  knowledge  which  is  of 
supreme  interest,  since  it  covers  the  matters  of 
which  our  own  bodies  are  constructed,  the  foods  which  we 
eat  and  the  beverages  which  we  drink,  besides  a  host  of 
other  things  of  great  value  to  us. 

Although  the  old  division  of  chemistry  into  inorganic 
and  organic  is  still  kept  up  as  a  matter  of  convenience,  the 
old  boundaries  between  the  two  have  become  largely  obliter- 
ated. The  distinction  arose  from  the  fact  that  there  used 
to  be  (and  are  still  to  a  very  great  extent)  a  number  of  highly 
complex  substances  the  composition  of  which  is  known, 
for  they  can  be  analysed,  or  taken  to  pieces,  but  which  the 
wit  of  man  has  failed  to  put  together.  Consequently  these 
substances  could  only  be  obtained  from  organic  bodies. 
The  living  trees,  or  animals,  could  in  some  mysterious  way 
bring  these  combinations  about,  but  man  could  not.  The 
molecules  of  these  substances  are  much  more  complicated 
than  those  with  which  the  inorganic  chemist  deals.  The 
important  ingredient  in  them  all  is  carbon,  which  with 
hydrogen,  nitrogen  and  oxygen  almost  completes  the  list 
of  the  simple  elements  of  which  these  marvellous  substances 
are  compounded.  In  some  cases  there  appear  to  be  hundreds 
of  atoms  in  the  molecule. 

If  one  takes  a  glance  at  a  text -book  on  organic  chemistry 
the  pages  are  seen  to  be  sprinkled  all  over  with  C's  and  O's, 
N's  and  H's,  with  but  an  occasional  symbol  for  some  other 
element. 

Another  feature  of  this  branch  which  cannot  fail  to  strike 

42 


THE  FUEL  OF  THE  FUTURE  43 

the  casual  observer  is  the  queer  names  which  many  of  the 
substances  possess.  Trimethylaniline,  triphenylmethane  and 
mononitrophenol  are  a  few  examples  which  happen  to  occur 
to  the  memory,  and  they  are  by  no  means  the  longest  or 
queerest-sounding. 

Another  peculiarity  about  these  organic  substances  is 
that  a  number  of  them,  each  quite  different  from  the  others, 
can  be  formed  of  the  same  atoms.  Certain  atoms  of  hydrogen, 
sulphur  and  oxygen  form  sulphuric  acid,  and  under  whatever 
conditions  they  combine  they  never  form  anything  else. 
On  the  other  hand,  there  are  sixty-six  different  substances 
all  formed  of  eight  of  carbon,  twelve  of  hydrogen  and  four 
of  oxygen.  This  can  only  mean  that  in  such  cases  as  the 
latter  the  atoms  have  different  groupings  and  that  when 
grouped  in  one  way  they  form  one  thing,  in  another  way  some 
other  thing,  and  so  on.  This  explains  the  extreme  difficulty 
which  the  chemist  finds  in  building  up  some  of  these  organic 
substances. 

Every  now  and  again  we  are  startled  by  some  eminent 
man  stating  that  the  time  will  come  when  we  shall  be  able 
to  make  living  things,  when  the  laboratory  will  turn  out 
living  cows  and  sheep,  birds  and  insects,  even  man  with  a 
mind  and  soul  of  his  own.  Yet  one  cannot  but  feel  that 
such  men,  no  matter  how  great  their  authority,  are  simply 
"  pulling  the  public's  leg,"  to  use  a  colloquial  expression. 
For  they  hopelessly  fail  to  make  many  of  the  commonest 
things.  In  many  cases  where  they  wish  to  produce  an 
organic  substance  they  have  to  call  in  the  aid  of  some  living 
thing  to  do  it  for  them,  even  if  it  be  but  a  humble  microbe. 
For  the  microbes  perform  wonderful  feats  in  chemistry,  far 
surpassing  those  of  the  most  eminent  men.  Hence  the 
latter  very  sensibly  use  the  microbe,  employ  it  to  work  for 
them,  just  set  things  in  order  and  then  stand  by  while  the 
microbe  does  the  work. 

Thus  most  things  can  be  analysed — that  is  to  say,  taken  to 
pieces — while  many  things  can  now  be  synthesised — that 
is  to  say,  built  up  from  their  constituent  atoms — but  still  a 


44  THE  FUEL  OF  THE  FUTURE 

great  many  remain,  and  among  them  the  most  important,  the 
synthesis  of  which  completely  baffles  man.  One  of  the  most 
useful  and  widespread  substances,  for  example,  cellulose, 
is,  at  present  at  least,  utterly  beyond  us.  We  do  not  even 
know  how  many  atoms  there  are  in  the  cellulose  molecule. 
The  molecules  may,  for  all  we  know,  contain  thousands  of 
atoms.  Indeed  many  of  these  organic  matters  have  very 
large  molecules. 

And  even  if  the  chemist  were  able  to  make  all  kinds  of 
organic  matter,  he  would  still  be  as  far  off  as  ever  from 
making  living  matter.  Indigo  used  to  be  derived  entirely 
from  plants  of  that  name.  One  of  the  greatest  triumphs 
of  the  organic  chemist  was  when  he  produced  artificial  or 
synthetic  indigo.  But  he  is  as  far  off  as  ever  from  making 
the  indigo  plant.  It  is  claimed  that  "  synthetic  "  rubber 
is  exactly  the  same  as  natural  rubber,  although  some  users 
say  it  is  not  quite  the  same.  Still,  if  it  be  so,  it  is  dead 
rubber,  not  the  living  part  of  the  plant.  The  time,  then,  is 
infinitely  far  distant  when  the  chemist  will  be  able  to  make 
anything  with  the  characteristics  of  life — namely,  to  grow 
by  accretion  from  within  and  to  reproduce  its  kind.  The 
most  wonderful  product  of  the  laboratory  is  dead.  At  most 
it  simply  resembles  something  which  once  was  alive. 

But  that  is  somewhat  of  a  digression.  This  dissertation 
on  organic  chemistry  was  simply  intended  to  lead  up  to  the 
question  of  liquid  fuels,  all  of  which  are  organic. 

In  the  life  of  to-day  one  of  the  most  important  things  is 
petroleum.  This  is  a  kind  of  liquid  coal.  Just  how  it  was 
formed  down  in  the  depths  of  the  earth  is  not  clear.  One 
idea  is  that  it  is  due  to  the  decomposition  of  animal  and 
vegetable  matter.  Another  is  that  certain  volcanic  rocks 
which  are  known  to  contain  carbide  of  iron  might,  under 
the  influence  of  steam,  have  in  bygone  ages  given  off 
petroleum,  or  paraffin,  to  use  the  other  name  for  the  same 
thing. 

In  many  parts  of  the  world  these  deposits  of  oil  are  obtained 
by  sinking  wells  and  pumping  up  the  oil.  In  others  the 


THE  FUEL  OF  THE  FUTURE  45 

liquid  gushes  out  without  the  necessity  of  pumping  at  all. 
This  is  believed  to  be  due  to  the  fact  that  water  pressure  is 
at  work.  Artesian  wells,  from  which  the  water  rushes  of  its 
own  accord,  are  quite  familiar,  and  are  due  to  the  fact  that 
some  underground  reservoir  tapped  by  the  well  is  fed  through 
natural  pipes,  really  fissures  in  the  rock,  from  some  point 
higher  than  the  mouth  of  the  well.  Now  supposing  that  a 
reservoir  of  oil  were  also  in  communication  with  the  upper 
world  in  the  same  way,  the  descending  water  would  go  to 
the  bottom,  underneath  the  lighter  oil,  and  would  thus  lift 
it  up,  so  that  on  being  tapped  the  oil  would  rush  out. 

Another  source  of  mineral  oil  is  shale,  such  as  is  to  be 
found  in  vast  deposits  in  the  south-east  of  Scotland.  This 
shale  is  mined  much  as  coal  is  :  it  is  then  heated  in  retorts 
as  coal  is  heated  at  the  gas-works  :  and  the  vapour  which 
is  given  off,  on  being  condensed,  forms  a  liquid  like  crude 
petroleum. 

In  all  these  cases  the  original  oil  is  a  mixture  of  a  great 
number  of  grades  differing  from  each  other  in  various  ways. 
They  are  all  "  hydro-carbons,"  which  means  compounds 
of  carbon  and  hydrogen,  and  they  extend  from  cymogene 
(the  molecules  of  which  contain  four  atoms  of  carbon  and 
ten  of  hydrogen)  to  paraffin  wax,  which  has  somewhere  about 
thirty-two  of  carbon  to  sixty-six  of  hydrogen.  For  practical 
purposes  their  most  important  difference  is  the  temperature 
at  which  they  boil,  or  turn  quickly  into  vapour. 

This  forms  the  means  by  which  they  are  sorted  out.  In 
a  huge  still,  like  a  steam-boiler,  the  crude  or  mixed  oil  is 
gradually  heated,  and  the  gas  given  off  is  led  to  a  cooling 
vessel  where  it  is  chilled  back  into  liquid.  The  lightest  of 
all,  cymogene,  is  given  off  even  at  the  freezing-point  of  water. 
That  is  led  into  one  chamber  and  condensed  there.  Then, 
as  the  temperature  rises  to  18°  C.,  rhigolene  is  given  off : 
that  is  collected  and  condensed  in  another  vessel.  Between 
70°  and  120°  petroleum  ether  and  petroleum  naphtha  are 
produced,  and  they  together  constitute  what  is  commonly 
called  petrol.  Between  120°  and  150°  petroleum  benzine 


46  THE  FUEL  OF  THE  FUTURE 

arises.  All  the  foregoing  taken  together  constitute  about 
8  to  10  per  cent,  of  the  whole  crude  oil.  Then  between  150° 
and  300°  there  comes  off  the  great  bulk  of  the  oil,  nearly  80 
per  cent.,  the  kerosene  or  paraffin  which  we  burn  in  lamps. 
Above  300°  there  is  obtained  another  oil,  which  is  used  for 
lubrication,  also  the  invaluable  vaseline,  and  finally,  when 
the  still  is  allowed  to  cool,  there  remains  a  solid  residuum 
known  as  paraffin  wax.  This  process  is  known  as  fractional 
distillation,  and  it  will  be  noticed  that  it  consists  essentially 
in  collecting  and  liquefying  separately  those  vapours  which 
are  given  off  at  different  ranges  of  temperature.  For  our 
purpose  in  this  chapter  we  are  mainly  concerned  with  the 
petrol  and  the  kerosene. 

Many  efforts  have  been  made  in  times  gone  by  to  use 
kerosene  for  firing  the  boilers  of  steam-engines.  In  naval 
vessels  a  great  deal  is  so  used  at  the  present  time.  But 
the  chief  method  of  employing  oil  for  generating  power  is 
to  use  it  in  an  internal  combustion-engine.  These  machines 
have  been  dealt  with  at  length  in  Engineering  of  To-day  and 
Mechanical  Inventions  of  To-day  and  so  must  be  simply 
mentioned  here.  They  consist  of  two  types.  In  one, 
which  is  exemplified  by  the  ordinary  car  or  bicycle  motor, 
the  oil  is  gasified  in  a  vessel  called  a  carburetter  or  vaporiser 
and  then  led  into  the  cylinder  of  the  engine,  together  with 
the  necessary  air  to  enable  it  to  burn.  At  the  right  moment 
a  spark  ignites  the  mixture,  which  burns  suddenly,  causing 
a  sudden  expansion,  in  other  words,  an  explosion.  Thus  the 
power  of  the  engine  is  derived  from  a  succession  of  explosions. 
If  the  fuel  be  petrol  it  vaporises  at  the  ordinary  temperature 
of  the  engine  and  needs  no  added  heat.  With  kerosene, 
however,  heat  has  to  be  employed  in  the  vaporiser  to  make 
it  turn  readily  into  a  gas. 

The  other  method  is  employed  in  engines  of  the  new 
"  Diesel  "  type,  in  which  the  cylinder  of  the  engine,  being 
already  filled  with  hot  air,  has  a  jet  of  oil  sprayed  into  it. 
The  heat  of  the  air  causes  it  to  burst  into  flame,  causing  an 
expansion  which  drives  the  engine. 


THE  FUEL  OF  THE  FUTURE  47 

An  important  feature  in  the  latter  type  of  engine  is  that 
the  oil  is  very  completely  burnt,  so  that  very  heavy  oils  can 
be  used,  oils  which,  if  employed  in  an  engine  of  the  other 
kind,  would  choke  up  the  cylinder  with  soot.  In  other  words, 
the  range  of  oils  which  can  be  used  in  this  new  kind  of  engine 
is  much  wider  than  is  possible  in  the  others.  The  latter 
may  be  likened  to  a  fastidious  man  who  is  very  particular 
about  his  food,  while  the  former  resembles  the  man  of 
hearty  appetite  who  can  eat  anything.  And  just  as  a  man 
of  the  latter  sort  is  more  easily  provided  for  by  the  domestic 
authorities,  so  the  Diesel  engine  makes  the  problem  of  the 
provision  of  liquid  fuel  much  simpler. 

For  it  must  never  be  forgotten  that  the  provision  of  liquid 
fuel  for  the  world  is  by  no  means  a  simple  matter,  since  the 
supply  is  by  no  means  adequate.  The  output  runs  into 
thousands  of  millions  of  gallons,  and  the  whole  world  is 
being  searched  for  new  fields  of  oil,  and  yet  it  is  all  swallowed 
up  as  fast  as  it  can  be  produced,  while  the  coal  mines  do  not 
feel  the  competition.  A  year  or  so  ago  the  United  States 
and  Russia  between  them  (and  they  are  the  greatest  pro- 
ducers) obtained  5,000,000,000  gallons  of  oil,  seemingly  an 
enormous  quantity.  But,  on  the  other  hand,  Great  Britain 
alone  produces  over  250,000,000  tons  of  coal  per  annum. 
If,  therefore,  liquid  fuel  is  to  displace  coal,  as  some  people 
lightly  think  it  is  going  to  do,  the  supply  will  have  to  be 
multiplied  many  times.  In  the  amount  of  heat  which  it  is 
capable  of  giving  the  coal  of  Great  Britain  alone  beats  the 
oil  produced  by  the  whole  world. 

And  another  thing  to  be  borne  in  mind  is  that  as  the 
coal  miner  goes  down  to  the  seam  and  sees  for  himself  what 
is  there,  while  the  oil  producer  simply  stays  at  the  surface 
and  draws  it  up  with  a  pump,  the  coal  man  knows  far  more 
as  to  how  much  there  is  still  left  than  the  oil  man  does. 
We  know  that  the  coal  deposits  will  last  for  many  years 
to  come,  even  if  the  production  go  on  increasing,  whereas 
the  oil  supply  may  fall  off  in  the  near  future  instead  of 
increasing. 


48  THE  FUEL  OF  THE  FUTURE 

And  in  both  cases  we  are  using  up  capital.  Coal  is  not 
being  made  on  the  earth  now,  at  any  rate  in  any  appreciable 
quantity.  The  stage  of  the  earth's  history  favourable  to 
the  formation  of  coal  mesaures  has  long  gone  by.  And  the 
same  probably  applies  to  oil. 

It  is  interesting  in  this  connection  to  note  that  coal  itself 
is  to  a  certain  extent,  or  can  be  at  all  events,  a  source  of  oil. 
When  coal  is  heated  in  order  to  make  it  give  up  its  gas,  or 
to  turn  it  into  coke,  vapours  are  given  off  which  on  cooling 
become  coal-tar.  At  one  time  regarded  only  as  a  crude  sort 
of  paint,  this  is  now  the  source  from  which  many  chemical 
substances  are  obtained,  varying  from  photographic  chemi- 
cals to  saccharine,  a  substitute  for  sugar.  So  valuable  are 
these  products  that  there  is  a  brisk  demand  for  the  tar,  in 
other  directions  than  the  manufacture  of  oils,  but  oils  of 
various  kinds  are  also  obtained  from  it. 

The  first  step  in  the  operations  is  fractional  distillation, 
after  the  manner  just  described  for  petroleum.  The  first 
"  fraction  "  is  "  coal-tar  naphtha."  Then  follows  "  carbolic 
oil,"  after  that  "  heavy"  or  "  creosote  oil,"  anthracene  oil, 
and  finally  there  remains  in  the  still  on  cooling  a  solid 
residue  known  as  coal-pitch.  The  naphtha,  on  being 
distilled  again,  gives,  among  other  things,  benzine,  from 
which  the  famous  aniline  dyes  are  made,  and  which  is  use- 
ful in  many  industries.  Creosote  is  largely  employed  as  a 
preservative  for  wood,  being  forced  into  the  timber  under 
high  pressure,  so  that  it  penetrates  right  into  it  and  tends 
to  prevent  rotting,  no  matter  how  wet  it  may  be.  Railway 
sleepers  are  thus  treated,  small  truck-loads  of  them  being 
run  into  a  cast-iron  tunnel  which  is  then  sealed  at  both  ends, 
while  the  creosote  is  forced  in  by  powerful  pumps.  After 
such  treatment  they  can  lie  nearly  buried  in  the  damp 
ballast  for  a  long  time  without  any  deterioration. 

These  coal-tar  substances  are  all  very  similar  to  petroleum 
and  its  products,  hydrocarbons,  compounds  of  hydrogen 
and  carbon  in  various  proportions.  Many  of  them  could 
be  used  for  fuel. 


By  permission  of  Dupont  Powder  Co. 

APPLE  TREE  PLANTED  WITH  A  SPADE 

This  apple  tree  was  planted  in  the  ordinary  way  with  a  spade.     Compare  its  size 
with  that  in  following  illustration  at  p.  48. 


THE  FUEL  OF  THE  FUTURE  49 

But  since  they  are  based  upon  the  supply  of  coal,  which 
is  itself  limited,  they  cannot,  however  they  may  be  used, 
do  more  than  stave  off  the  evil  day  when  the  supply  will  be 
exhausted. 

Quite  different  is  it  with  alcohol,  which  it  seems  likely 
may  be  the  fuel  of  the  future.  Some  people  will  be  inclined 
to  exclaim  "  What  a  pity  to  burn  it ! "  since  to  many  the  word 
conveys  ideas  of  another  sort  altogether.  There  are  many 
nowadays,  however,  who,  like  the  writer,  have  none  but  a 
scientific  interest  in  it.  To  such  whisky,  for  example,  is 
but  "  impure  "  alcohol,  and  it  is  without  the  "  impurities  " 
that  it  may  become  of  vast  use  to  the  world,  thereby  possibly 
repaying  man  for  some  of  the  harm  which  in  the  past  it  has 
inflicted  upon  him. 

Alcohol,  again,  is  a  hydrocarbon.  It  is  really  more  correct 
to  speak  of  it  in  the  plural,  as  "alcohols,"  since  there  is  a 
large  group  of  substances  all  of  the  same  name.  Two  of 
these  are  of  the  greatest  importance,  methyl  alcohol  and  ethyl 
alcohol.  The  former  is  obtained  from  wood,  hence  it  is 
sometimes  called  wood  spirit.  Wood  is  strongly  heated  in 
an  iron  still,  and  the  methyl  alcohol  is  given  off  in  the  form 
of  vapour,  which  on  being  collected  and  cooled  condenses 
into  liquid.  It  is  exceedingly  unpleasant  to  the  taste  :  if 
it  were  the  only  kind  there  would  be  no  consumption  of 
alcohol  as  a  drink. 

The  second  kind  mentioned  is  obtained  by  the  agency  of 
germs  or  microbes,  and  the  story  of  its  production  is  so 
interesting  as  to  demand  a  little  space. 

We  will  commence  with  the  maltster.  He  performs 
the  first  part  of  the  operation.  Starting  with  ordinary 
barley,  by  the  action  of  heat,  aided  by  natural  growth,  he 
produces  the  raw  material  on  which  the  brewer  may  work. 
Now  barley,  like  all  grain,  is  largely  made  up  of  starch,  and 
although  starch  will  not  make  alcohol,  it  can  be  turned  into 
sugar,  which  will.  So  the  task  of  the  maltster  is  to  commence 
the  change  of  the  starch  in  the  grain  into  sugar. 

First  of  all  it  is  soaked  in  water  and  spread  upon  floors 


50  THE  FUEL  OF  THE  FUTURE 

and  heated  until  it  begins  to  sprout.  There  is  a  little  part 
in  each  grain  called  the  endosperm,  which  is  the  embryonic 
plant,  and  the  starch  is  really  the  food  provided  by  nature 
to  nourish  the  growing  endosperm  until  such  time  as  it 
shall  be  strong  enough  to  draw  its  nourishment  from  the  soil. 
In  order  that  it  may  not  be  washed  away  prematurely,  the 
starch  is  locked  up  by  nature  in  closely  fastened  cells,  and, 
moreover,  it  is  insoluble,  so  that  water  cannot  carry  it  away. 
The  endosperm,  however,  has  at  its  disposal  certain  sub- 
stances known  as  enzymes  (and  it  increases  its  store  of  these 
as  it  grows),  one  of  which  is  able  to  dissolve  away  the  walls 
of  the  cells,  to  unlock  the  treasures,  as  it  were,  while  the 
other  turns  the  insoluble  starch  into  soluble  matter,  in 
which  state  the  growing  organism  is  able  to  make  use  of 
it  as  food. 

So  as  the  grain  sprouts  upon  the  maltster's  floor  this  pro- 
cess is  going  on — the  cells  are  being  opened  and  their  contents 
converted  from  starch  into  soluble  matters.  Then,  when  the 
growth  has  gone  far  enough,  the  grain  is  transferred  to  a 
kiln,  where  it  is  subjected  to  heat,  by  which  the  growth  is 
stopped.  The  living  part  of  the  grain  is,  in  fact,  killed. 
That  is  mainly  to  stop  the  young  plant  from  eating  up  the 
altered  starch,  which  it  would  do  if  allowed  time,  but  which 
the  brewer  wants  to  be  kept  for  his  own  use. 

The  maltster's  task  is  now  finished,  and  we  come  to  the 
brewer's.  The  first  thing  he  does  with  the  malt  is  to  crush 
it  between  rolls,  thereby  liberating  thoroughly  those  sub- 
stances which  have  been  formed  from  the  starch  and  which 
he  intends  to  turn  into  sugar.  Having  crushed  it,  he  places 
it  in  the  "  mash  tun,"  a  large  tank  of  wood  or  iron,  in  which 
it  is  mixed  with  water  and  subjected  to  heat.  While  in 
this  vessel  the^  enzymes  become  active  again  and  turn  the 
soluble  starch,  or  a  part  of  it,  into  a  kind  of  sugar. 

The  liquid  drawn  off  from  the  mash  tun,  containing,  of 
course,  the  sugar,  is  subsequently  boiled,  numerous  flavour- 
ing matters  (including  hops)  are  added,  and  then  it  is  cooled 
again,  ready  for  the  final  process — fermentation. 


THE  FUEL  OF  THE  FUTURE  51 

This  takes  place  in  a  largo  vat  or  "  tun  "  and  is  brought 
about  by  the  agency  of  yeast  which  is  added  to  the  liquid. 

Now  yeast  is  a  multitude  of  microscopic  plants  round  in 
shape  and  about  one  three-thousandth  of  an  inch  in  diameter. 
Though  so  small,  this  little  organism  is  really  quite  com- 
plicated in  its  structure,  and  within  its  little  body  there 
are  carried  on  complicated  chemical  changes  which  baffle 
entirely  the  most  learned  chemist  to  imitate.  Further,  he 
has  yet  to  find  out  how  the  little  yeast  plant  does  it.  He 
not  only  cannot  imitate  the  process,  he  does  not  know  what 
the  process  is.  These  little  organisms  multiply  mainly  by 
the  process  of  "  budding."  A  new  one  grows  out  of  the 
side  of  each  old  one,  rapidly  reaches  maturity,  breaks  away 
and  commences  an  independent  existence.  No  sooner  is  it 
free  than  it  in  turn  gives  birth  to  another.  Indeed  so  great 
is  its  hurry  to  propagate  itself  that  sometimes  the  new  cell 
begins  to  throw  out  a  bud  before  it  has  itself  separated  from 
its  parent.  It  is  therefore  easy  to  see  that  yeast  increases 
in  quantity  by  what  some  call  "  leaps  and  bounds,"  but 
which  the  mathematically  minded  know  as  geometrical 
progression. 

The  particular  form  of  sugar  with  which  we  are  concerned 
here  is  known  as  "  dextro-glucose."  This  the  yeast  splits 
up  into  alcohol  and  carbonic  acid  gas.  The  latter  bubbles 
up  to  the  surface,  and  escapes  into  the  air,  while  the  alcohol 
becomes  dissolved  in  the  watery  liquid.  It  is  believed  that 
the  yeast  performs  this  operation  not  directly,  but  by  the 
production  of  certain  enzymes,  which  in  their  turn  act  upon 
the  sugar. 

The  liquid  so  formed  is  beer.  But  since  it  is  alcohol  with 
which  we  are  concerned,  and  not  beer,  many  details  con- 
nected with  its  manufacture  have  been  omitted.  Enough 
has  been  said,  however,  to  show  that  by  comparatively 
simple  processes  grain  of  all  sorts,  in  fact,  anything  which 
contains  starch,  and  such  things  are  to  be  found  in  world- 
wide profusion,  can  be  turned  into  alcohol.  All  the  really 
intricate  chemical  functions  are  performed  readily  and 


52  THE  FUEL  OF  THE  FUTURE 

cheaply  by  living  organisms.  All  man  has  to  do  is  to  set 
up  the  conditions  under  which  the  organisms  can  work. 

In  the  process  just  described  only  a  portion  of  the  starch 
in  the  grain  is  converted  into  sugar,  hence  the  percentage  of 
alcohol  in  beer  is  comparatively  small.  If  all  the  starch 
be  converted  a  liquid  much  stronger  in  alcohol  is  produced, 
and  if  that  be  distilled,  so  as  to  separate  the  spirit  from  the 
water  with  which  it  is  mixed,  there  results  whisky.  Brandy, 
likewise,  is  the  spirit  distilled  from  wine,  rum  from  molasses, 
and  so  on.  In  all  these  familiar  beverages  the  essential 
feature  is  this  same  alcohol,  of  the  variety  knowrn  as  ethyl 
alcohol. 

It  will  be  noticed  that  in  the  making  of  beer  the  alcohol 
is  actually  formed  in  water.  There  is  a  sugary  water  which 
under  the  action  of  the  yeast  becomes  an  alcoholic  water. 
And  this  indicates  a  very  useful  feature  about  the  liquid 
when  used  for  industrial  purposes.  A  tank  full  of  petrol  is 
extremely  dangerous,  so  much  so  that  the  storage  of  petrol 
is  hedged  about  by  all  manner  of  precautions.  The  danger 
is  that  it  gives  off  an  inflammable  vapour  and  that  if  it  once 
begin  to  burn  there  is  practically  no  possibility  of  putting 
it  out.  Being  lighter  than  water,  it  simply  clothes  with  a 
layer  of  fire  any  water  which  may  be  thrown  on  to  it.  The 
water  in  such  circumstances  simply  serves  to  spread  the 
flaming  petrol  about  and  so  to  make  matters  worse.  Now 
alcohol,  with  its  partiality  for  the  companionship  of  water, 
behaves  quite  differently.  True,  it  also  may  give  off  an 
inflammable  vapour,  but  if  a  quantity  of  it  catch  fire  it  can 
be  extinguished  in  the  usual  way  by  a  fire-engine.  The 
water  and  alcohol  immediately  combine — the  alcohol  be- 
comes dissolved  in  the  water  just  as  sugar  may  do,  and  as 
soon  as  the  percentage  of  water  in  the  mixture  becomes 
considerable  the  burning  stops. 

It  may  be  that  some  readers  will  have  discovered  this 
fact  for  themselves  without  knowing  precisely  what  it  was. 
It  is  a  common  dodge  with  amateur  photographers  if  they 
want  to  dry  a  negative  quickly  to  immerse  it  in  methylated 


THE  FUEL  OF  THE  FUTURE  53 

spirit.  The  spirit  seems  to  take  the  water  out  of  the  film 
and,  itself  drying  quickly,  leaves  the  negative  in  a  perfectly 
dry  condition  in  a  few  minutes.  Now  after  using  spirit 
in  that  way  it  is  useless  to  put  it  in  a  spirit  stove  or  lamp. 
It  will  not  burn.  Methylated  spirit  is  alcohol,  and  the 
reason  why  it  has  such  a  quick  drying  action  is  that  it  and 
the  water  in  the  wet  film  quickly  mix.  After  immersion 
the  film  is  wet,  not  with  water  merely,  but  with  a  mixture 
of  a  lot  of  spirit  and  a  little  water.  Hence  the  speed  with 
which  it  evaporates.  And  the  non-inflammability  of  the 
mixture  is  due  to  the  presence  of  the  water. 

Methylated  spirit  only  differs  from  the  alcohol  in  alcoholic 
beverages  in  that  something  is  added  to  make  it  undrinkable. 
Owing  to  the  craving  for  it,  which  is  so  widespread,  and  the 
doubtful  effect  which  it  has  on  certain  citizens,  most  states 
regard  it  as  pre-eminently  a  subject  for  taxation,  thereby 
on  the  one  hand  bringing  in  a  good  revenue,  and  on  the  other 
discouraging  its  too  free  use.  But  those  considerations 
apply  only  to  drinkable  alcohol.  That  which  is  to  be  used 
for  industrial  purposes  is  not  in  any  way  a  legitimate  object 
for  taxation.  Hence  the  problem  arises  of  making  a  form 
of  alcohol  which  shall  answer  all  the  needs  of  the  industries 
which  use  it,  and  at  the  same  time  be  so  repulsive  to  the 
senses  that  no  one  can  possibly  drink  it.  This  result  is 
achieved  by  adding  some  of  the  methyl  alcohol  derived  from 
the  vapour  given  off  by  wood  when  heated.  Commonly 
known  as  "  wood  spirit,"  this  is  so  unpleasant  that  it  renders 
the  mixture  of  no  use  for  drinking,  and  so  it  can  safely  be 
freed  from  taxation. 

Unfortunately  this  spirit  has  less  heating  value  than 
petrol.  That  means  that  a  given  quantity  of  each  liquid 
will  produce  more  heat  in  the  case  of  petrol  than  in  the  case 
of  alcohol.  Indeed  the  difference  is  about  two  to  one. 
Hence  an  engine  to  give  out  a  certain  horse-power  would 
need  to  have  its  cylinders  twice  as  big  if  it  were  to  use  alcohol 
instead  of  the  other  fuel.  There  is  a  certain  compensation, 
however,  in  the  fact  that  alcohol  is  very  easily  compressible. 


54  THE  FUEL  OF  THE  FUTURE 

In  modern  internal  combustion-engines  much  of  the  efficiency 
is  due  to  the  explosive  charge  which  is  drawn  into  the  cylinder 
being  compressed  into  a  small  space  before  it  is  fired.  It 
was  the  discovery  of  the  value  of  compressing  the  gas  which 
made  the  gas-engine  so  formidable  a  rival  to  the  steam- 
engine,  and  the  wonderful  performances  of  the  Diesel  engines 
are  due  very  largely  to  the  fact  that  the  air  is  compressed 
in  the  cylinder  to  a  very  high  pressure.  The  jet  of  oil  burns 
in  highly  compressed  air.  And  because  of  the  facility  with 
which  alcohol  can  be  compressed  it  is  said  to  be  more 
effective  as  a  source  of  motive  power  than  would  be  expected 
from  its  comparatively  feeble  heat. 

Thus  we  may  sum  up  the  possibilities  of  the  future.  Coal, 
petroleum  and  their  derivatives  exist  in  limited  quantities 
in  the  world,  and  so  far  as  we  can  see  the  vast  drafts  which 
we  are  taking  from  them  are  not  being  replaced,  indeed  at 
this  stage  of  the  earth's  development  cannot  be  replaced,  by 
any  more.  Sooner  or  later  we  must  come  to  an  end  of  them. 
Is  it  not  comforting,  therefore,  to  know  that  there  is  another 
source  of  fuel  at  hand,  inexhaustible,  since  it  can  be  pro- 
duced as  needed.  We  have  only  to  set  the  sun  and  the 
ground  to  work  to  produce  grain,  rice,  potatoes,  or  any  of  the 
myriad  substances  which  contain  starch,  and  from  that,  by 
simple  and  well-known  processes,  we  can  obtain  a  cheap, 
safe  and  reliable  fuel.  Indeed  there  seems  nothing  but  the 
ultimate  loss  of  sunlight,  countless  millions  of  years  hence, 
which  can  ever  check  the  supply  of  this  valuable  commodity. 
What  has  doubtless,  in  many  cases,  been  a  curse  in  the  past 
may  turn  out  to  be  the  great  boon  of  the  future. 


CHAPTER  IV 

SOME  VALUABLE  ELECTRICAL  PROCESSES 

STUDENTS  of  that  branch  of  science  known  as 
physics  are  coming  to  the  conclusion  that  electricity 
plays  a  much  more  important  part  in  the  universe 
than  was  supposed.  They  are  led  to  believe  that  electrical 
attraction  is  the  cement  which  binds  together  those  exceed- 
ingly minute  particles  out  of  which  everything  is  built  up. 
Whether  electricity  binds  them  together  or  not,  it  is  certain 
that  electrical  action  can  in  some  cases  separate  those 
particles,  and  this  process  of  separation  provides  a  means 
of  carrying  on  some  very  remarkable  and  useful  industrial 
processes. 

Let  us  imagine  a  vessel  filled  with  water  to  which  has  been 
added  a  little  sulphuric  acid,  while  suspended  in  it  are  two 
strips  of  platinum.  There  is  a  space  between  the  strips, 
so  that  when  their  upper  ends  are  suitably  connected  to 
a  source  of  electric  current  that  current  flows  from  one 
strip  to  the  other  through  the  liquid. 

That  is  an  example  of  the  apparatus  for  carrying  out  this 
electrical  separation  in  its  simplest  form,  and  it  will  facilitate 
the  further  description  if  the  names  of  various  parts  are 
enumerated. 

The  process  itself  is  electrolysis  ;  the  liquid  is  the  electro- 
lyte, while  the  strips  are  the  electrodes.  The  individual 
electrodes,  again,  have  special  names,  that  by  which  the 
current  enters  being  the  anode  and  that  by  which  it  leaves 
the  cathode.  It  is  not  difficult  to  remember  which  is  which 
if  we  bear  in  mind  that  the  current  traverses  them  in  alpha- 
betical order.  Since,  however,  it  may  not  be  easy  for  the 
general  reader  to  carry  all  these  terms  in  his  mind,  we  will, 

55 


56  SOME  VALUABLE  ELECTRICAL  PROCESSES 

when  it  is  necessary  to  differentiate  between  the  two 
electrodes,  call  one  the  in-electrode  and  the  other  the 
out-electrode. 

Returning  now  to  our  imaginary  apparatus,  let  us  turn 
on  the  current.  At  first  nothing  seems  to  be  happening, 
although  suitable  instruments  would  show  that  current 
was  flowing.  Soon,  however,  little  bubbles  appear  upon  the 
electrodes,  and  these  grow  larger  and  larger,  until  they 
detach  themselves  from  the  platinum  to  which  they  have 
been  adhering,  float  up  to  the  surface  and  burst.  The 
question  which  naturally  arises  is,  What  do  those  bubbles 
consist  of  ?  Are  they  air  ? 

If  we  take  means  to  collect  the  gases  which  formed  them 
we  get  an  unmistakable  answer.  The  bubbles  which  arise 
from  the  in-electrode  are  oxygen,  those  from  the  other 
hydrogen.  If  we  allow  our  apparatus  to  work  for  some 
time,  and  collect  all  the  gas  which  arises,  we  shall  find  that 
there  is  twice  as  much  hydrogen  as  oxygen.  We  shall  also 
find,  as  the  process  goes  on,  that  the  quantity  of  water 
diminishes. 

Perhaps  I  may  be  allowed  at  this  point  to  remind  my 
readers  that  water  is  a  collection  of  minute  ultra-microscopic 
particles  called  "molecules,"  each  of  which  is  formed  of 
three  smaller  particles  still  called  "  atoms."  Of  the  three 
atoms  two  are  hydrogen  and  one  oxygen.  Water  therefore 
consists  of  hydrogen  and  oxygen,  there  being  twice  as  much 
of  the  former  as  there  is  of  the  latter. 

We  see,  therefore,  that  electrolysis  gives  us  hydrogen  and 
oxygen  in  exactly  those  proportions  in  which  they  occur 
in  water,  and  since  we  also  see  that  as  these  gases  appear 
the  water  itself  disappears,  we  are  led  to  conclude  that  the 
current  is  splitting  up  the  water  into  the  gases  of  which  it 
is  formed. 

But  the  strange  thing  is  that  this  will  not  work  with  pure 
water.  We  have  to  add  something  to  it.  In  the  case  of 
our  imaginary  experiment  it  was  sulphuric  acid.  What 
part  does  that  play  ? 


SOME  VALUABLE  ELECTRICAL  PROCESSES   57 

This  is  not  fully  understood,  but  we  may  be  able  to  form 
a  mental  picture  of  what  is  believed  to  happen  as  follows. 

The  in-electrode  is  surrounded  by  a  vast  assemblage  of 
these  tiny  molecules,  most  of  them  those  of  water,  but  a 
few  those  of  the  acid.  The  latter  are  more  complex  in  their 
structure  than  the  former,  but  they  too  contain  hydrogen. 
Current  flows  into  the  electrode  and  instantly  hydrogen 
atoms  from  the  acid  molecules  crowd  round  it,  like  boatmen 
at  the  seaside  anxious  to  secure  a  passenger.  Each  takes 
on  board  a  quantity  of  electricity  and  with  it  darts  across 
the  intervening  space  to  the  other  electrode.  Arrived  there, 
it  gives  up  its  load  and,  its  work  done,  remains  lying  upon 
the  electrode  until  enough  others  like  unto  itself  have 
gathered  there  to  form  a  bubble  and  so  escape.  These 
hydrogen  atoms  are  thought  to  be  the  craft  which  carry  the 
current  through  the  liquid  and  enable  it  to  pose,  as  it  were, 
as  a  conductor  of  electricity,  which  in  reality  it  is  not. 

But  where  does  the  oxygen  come  from  ? 

To  find  the  answer  to  that  we  must  add  a  second  chapter 
to  our  story.  When  the  hydrogen  "  boats  "  took  on  board 
their  load  of  electricity  they  left  their  former  associates, 
and  these  forthwith  "  set  upon  "  neighbouring  water  mole- 
cules and  with  the  audacity  of  highwaymen  stole  from  them 
enough  hydrogen  atoms  to  take  the  place  of  those  they  had 
lost.  Thus  the  acid  molecules  became  complete  once  more, 
while  the  scene  of  the  conflict  near  the  in-electrode  was 
strewn  with  the  remains  of  the  water  molecules  from  which 
the  hydrogen  atoms  had  been  stolen.  These  remains,  of 
course,  would  be  oxygen,  and  they,  collecting  together  on 
the  electrode,  would  eventually  be  in  numbers  sufficient 
to  form  bubbles  and  so  escape. 

Thus  it  may  be  the  acid  which  really  does  the  work,  yet 
because  of  its  subsequent  raid  upon  the  water  it  is  the  latter 
which  disappears,  and  it  is  the  materials  of  the  latter  which 
are  bought  to  the  surface  in  the  bubbles. 

And  there  we  see  the  mechanism  whereby,  so  it  is  believed, 
electric  current  can  pass  through  otherwise  non-conducting 


58      SOME  VALUABLE  ELECTRICAL  PROCESSES 

liquids.  And  the  important  point,  as  far  as  practical  utility 
is  concerned,  is  that  the  passage  of  the  current  is  accom- 
panied by  a  splitting  up  of  something  or  other,  either  the 
water  or  something  in  it,  the  materials  of  which  are  deposited, 
one  on  one  electrode  and  the  other  on  the  other. 

And  now  we  can  proceed  to  those  useful  applications  of 
electrolysis,  the  commonest  of  which,  perhaps,  is  electro- 
plating. 

We  have  seen  how  electrolysis  causes  hydrogen,  probably 
out  of  the  acid,  to  be  deposited  upon  one  electrode.  Suppose 
that,  instead  of  an  acid,  we  put  in  the  water  one  of  those 
substances  known  to  chemists  as  a  "  salt,"  the  commonest 
example  of  which  is  ordinary  table  salt.  This  well-known 
condiment  is  caused  by  the  interaction  of  hydrochloric  acid 
and  the  metal  sodium  and  will  serve  to  illustrate  what  all 
salts  are. 

All  acids  are  compounds  of  hydrogen  and  something  else, 
and  their  biting  action  is  due  to  the  readiness  with  which 
the  "  something  else  "  evicts  the  hydrogen  and  takes  in  a 
metal  in  its  place.  Thus  hydrochloric  acid,  given  the 
opportunity,  gets  rid  of  its  hydrogen  and  takes  in  sodium, 
thereby  forming  chloride  of  soda  or  common  salt. 

Another  example  is  the  gold  chloride  familiar  to  photog- 
raphers. This  is  the  result  of  the  action  of  certain  acids 
upon  gold,  wherein  the  acids  throw  out  their  hydrogen  and 
take  in  gold  instead. 

To  sum  up,  then,  a  salt  is  just  the  same  sort  of  thing  as 
an  acid,  like  the  sulphuric  acid  which  we  used  in  our  "  experi- 
ment," except  that  some  metal  has  taken  the  place  of  the 
hydrogen. 

It  is  not  surprising,  then,  to  find  that  if  we  put  a  salt  in 
the  electrolyte  instead  of  an  acid  we  get  a  similar  result. 
In  the  one  case  hydrogen  is  deposited  upon  the  out-electrode, 
in  the  other  the  metal.  In  the  former  case,  since  hydrogen 
is  a  gas,  it  forms  bubbles  and  floats  away,  but  in  the  latter 
the  solid  metal  remains  a  thin,  even  coating  upon  the 
electrode.  That  is  the  principle  of  electro-plating. 


SOME  VALUABLE  ELECTRICAL  PROCESSES   59 

The  electrolyte  consists  of  a  suitable  solution  containing 
a  salt  of  the  metal  to  be  deposited,  and  it  is  placed  in  an 
insulating  vessel  or  vat.  The  articles  to  be  plated  form  the 
out-electrode,  so  that  they  have  to  be  suspended  in  some 
convenient  way  from  a  metal  conductor  by  conducting  wires. 
Of  course  they  are  entirely  immersed  in  the  liquid.  The 
in-electrode  is  sometimes  a  plate  of  platinum  (the  reason 
that  expensive  metal  is  used  being  that  it  is  unaffected  by 
the  chemicals)  or  else  a  plate  of  the  metal  being  deposited. 
In  the  former  case,  the  solution  becomes  weaker  as  the  work 
proceeds,  and  more  salt  has  to  be  added.  In  the  latter, 
however,  the  strength  of  the  solution  remains  unchanged, 
for  by  an  interesting  interchange  the  in-electrode  adds  to  it 
just  what  it  loses  by  deposition  upon  the  other  one.  The 
effect  is  therefore  just  as  if  the  current  tore  off  particles 
from  the  one  and  placed  them  upon  the  other. 

This  is  believed  to  be  due  to  the  agency  of  the  oxygen 
which  in  the  case  of  the  electrolysis  of  water  becomes  free, 
but  which  in  this  case  forms  with  the  metal  electrode  a 
layer  of  oxide  upon  its  surface,  this  oxide  being  then  dis- 
solved away  by  the  liquid.  Thus  as  fast  as  the  metal  is 
deposited  upon  the  out-electrode  its  place  is  taken  by  more 
metal  from  the  in-electrode. 

In  some  processes  it  is  desired  to  deposit  metal  upon  a 
non-conducting  surface,  and  it  is  evident  that  such  cannot 
be  used  as  an  electrode.  Nor  is  it  any  use  to  attempt  to 
deposit  upon  anything  except  an  electrode.  The  only  thing 
to  do,  then,  is  to  make  the  object  a  conductor  by  some  means. 
Models  in  clay,  wax  and  plaster,  once-living  objects  like 
small  animals,  fruit,  flowers  or  insects,  can,  however,  have 
a  perfect  replica  made  of  them  by  electrical  deposition,  by 
the  simple  method  of  coating  the  surface  to  be  plated  with 
a  thin  layer  of  plumbago.  This  skin,  although  extremely 
thin,  is  a  sufficiently  good  conductor  to  make  the  process 
possible.  Process  blocks  for  printing  are  copied  in  this 
way,  so  that  a  particularly  delicate  example  of  the  block- 
maker's  art  need  not  be  worn  down  by  much  pressing, 


60   SOME  VALUABLE  ELECTRICAL  PROCESSES 

copies  or  "  electros  "  being  made  off  it  for  actual  use  in 
the  press. 

The  original  block  is  a  plate  of  copper  on  which  the  picture 
is  represented  by  minute  depressions  and  prominences.  On 
this  a  layer  of  soft  wax  is  pressed,  so  as  to  obtain  a  perfect 
but  reversed  copy.  Having  been  coated  with  plumbago^ 
this  is  then  put  into  a  vat  containing  a  solution  of  copper 
salts  and  is  used  as  the  out-electrode,  the  other  being  a 
plate  of  copper.  When  the  current  is  turned  on  the  copper 
is  thus  deposited  on  the  wax  until  a  thin  sheet  of  copper  is 
formed  which  is  an  exact  but  reversed  copy  of  the  wax, 
a  direct  copy,  that  is,  of  the  original  block. 

The  back  of  this  thin  sheet  is  then  covered  with  molten 
lead  or  type  metal  to  fill  up  any  depressions  and  to  give  it 
sufficient  strength.  Anyone  who  has  seen  one  of  these 
"  half-tone "  blocks  covered  with  minute  depressions  so 
slight  that  they  can  scarcely  be  seen,  yet  so  perfect  that  a 
beautiful  print  can  be  obtained  from  them,  will  realise  the 
wonderful  power  of  this  electrolytic  process,  the  marvellous 
accuracy  with  which  the  original  is  copied,  and  the  unerring 
way  in  which  the  electric  current  carries  the  particles  of 
copper  into  every  one  of  the  myriad  recesses  in  the  wax. 

Another  specimen  of  the  marvellous  work  of  this  system 
is  the  wax  cylinder  of  the  phonograph.  The  sound  is  pro- 
duced by  a  needle  trailing  along  a  groove  of  varying  depth 
cut  in  the  surface  of  the  cylinder.  This  groove  forms  a 
spiral,  passing  round  and  round  like  the  thread  of  a  screw, 
and  it  encircles  the  cylinder  one  hundred  times  in  every  inch 
of  its  length.  Consequently,  at  any  point  one  may  take, 
there  is  but  one  one-hundredth  of  an  inch  from  the  centre  of 
one  turn  to  the  centre  of  the  turn  on  either  side  of  it.  And 
at  its  deepest  the  groove  is  less  than  one-thousandth  of  an 
inch  deep.  The  phonograph  itself  cuts  the  first  "  master  " 
record,  as  it  is  termed,  and  the  problem  is  to  take  a  number 
of  casts  off  this  model  of  such  delicacy  and  accuracy  that 
every  variation  in  that  exceedingly  fine  groove  shall  be 
faithfully  reproduced.  Such  a  task  might  well  be  given  up 


SOME  VALUABLE  ELECTRICAL  PROCESSES  61 

as  hopeless,  but  With  the  help  of  electrolysis  it  is  accom- 
plished easily  and  cheaply. 

To  attempt  to  press  anything  upon  the  surface  of  the 
"  master  "  would  but  smooth  out  the  soft  wax  and  obliterate 
the  groove  altogether.  To  apply  anything  softened  by 
heating  would  be  to  melt  it.  But  electrolysis,  without 
tending  in  any  way  to  distort  or  damage  the  delicately  cut 
surface,  deposits  upon  it  a  surface  of  metal  from  which 
thousands  of  casts  can  be  made.  The  gentle  fingers  of  the 
electricity  overlay  the  soft  wax  with  the  hard,  strong  metal 
with  a  minute  perfection  almost  beyond  belief. 

To  commence  with,  the  master  record  is  placed  upon  a 
sort  of  turntable  in  a  vacuum  and  turned  round  in  the 
neighbourhood  of  two  strips  of  gold-leaf  strongly  electrified. 
By  this  means  the  gold  is  vaporised  and  a  perfect  coating 
of  gold  is  laid  upon  the  wax.  This  is  far  too  thin  to  be  of 
any  use,  except  to  render  the  cylinder  a  conductor,  for  the 
coating  is  so  fragile  that  it  is  no  stronger  than  the  wax  itself. 
It  enables  the  cylinder,  however,  to  be  electro-plated  with 
copper  until  it  is  surrounded  by  a  strong  metallic  shell  a 
sixteenth  of  an  inch  thick.  It  takes  about  four  days  to 
deposit  this  thickness.  The  copper  shell  is  then  turned 
smooth  in  a  lathe  and  fitted  tightly  into  a  brass  jacket.  A 
little  cooling  causes  the  wax  record  to  shrink  sufficiently 
to  free  it  from  the  copper  shell  and  allow  it  to  be  lifted  out. 
A  copper  mould  is  thus  formed  in  which  any  number  of 
additional  records  can  be  cast.  The  molten  wax  is  simply 
introduced  into  the  inside,  and  allowed  to  set ;  the  inside 
is  bored  out  in  a  lathe,  and  then  with  a  little  cooling  it 
shrinks  and  can  be  withdrawn,  a  completely  finished  record, 
every  tiny  depression  or  swelling  in  the  original  master 
being  reproduced  with  an  accuracy  almost  incredible. 

Another  valuable  use  to  which  this  process  is  put  is  the 
purification  of  metals.  The  electro-chemical  action  works 
with  unerring  precision  :  it  never  mistakes  an  atom  of  iron 
for  an  atom  of  copper,  for  example.  Passing  through  a 
solution  of  copper  salt,  the  current  deposits  only  copper. 


62      SOME  VALUABLE  ELECTRICAL  PROCESSES 

For  modern  electrical  machinery  and  apparatus  copper 
is  required  of  the  utmost  possible  purity,  for  every  impurity 
adds  to  its  electrical  resistance,  in  other  words,  diminishes 
its  value  as  a  conductor.  Consequently  thousands  of  tons 
of  "  electrolytic  "  copper,  as  it  is  termed,  are  produced  every 
year.  The  electrodes  used  are  plates  of  ordinary  copper. 
A  coating  of  pure  metal  is  deposited  by  electrolysis  upon 
the  out-electrode  from  the  other  one.  When  the  deposit  is 
thick  enough  the  out-electrode  is  taken  out  and  the  deposit 
torn  off  it,  the  union  between  the  two  being  sufficiently 
imperfect  for  this  to  be  done  without  difficulty.  The  metal 
of  which  the  in-electrode  is  made  has  already  been  purified 
by  other  processes,  until  it  contains  but  one  per  cent,  of 
foreign  matter,  and  by  this  means  even  that  small  percentage 
is  entirely  got  rid  of.  The  impurities  fall  to  the  bottom  of 
the  vessel  in  the  form  of  "  slime,"  which  is  periodically 
removed. 

And  not  only  is  electrolysis  thus  unerring  in  picking  out 
certain  atoms  from  among  a  mixture,  but  there  is  an  exact 
relation  between  the  work  done  and  the  quantity  of  current 
used.  Consequently  it  forms  a  very  exact  method  of 
measuring  currents.  The  method  of  measuring  current  by 
the  strength  of  the  magnetic  field  which  it  produces  has 
been  mentioned  already,  and  such  measurements  can  be 
checked  by  electrolysis.  Thus  the  practical  definition  of 
the  ampere  is  "  that  current  which  when  passed  through  a 
solution  of  silver  nitrate  in  water  will  deposit  silver  at  the 
rate  of  -001118  gramme  per  second." 

The  electric  accumulator  or  secondary  battery,  one  of  the 
most  useful  appliances,  is  the  result  of  electrolysis  reversed. 
Many  large  electric-lighting  plants  have  in  addition  to  their 
generating  machinery  a  large  battery  of  secondary  cells, 
which,  being  kept  charged,  are  able  to  help  the  machinery 
in  times  of  heavy  demand,  or  even  to  supply  the  whole 
current  needed  for,  say,  half-an-hour,  so  that  the  whole  of  the 
machinery  could,  in  the  event  of  an  accident,  be  shut  down 
for  that  time  and  the  supply  maintained  from  the  batteries. 


SOME  VALUABLE  ELECTRICAL  PROCESSES   63 

This  would  be  sufficient  in  many  cases  for  fresh  machinery 
to  be  brought  into  action  or  emergency  arrangements  to  be 
made. 

It  may  be  that  this  book  is  being  read  by  someone  seated 
serenely  in  his  arm-chair  while  engineers  and  workmen  at 
the  generating  station  are  working  in  frantic  haste  to  set 
right  some  sudden  breakdown  before  the  batteries  are  run 
down.  The  batteries  may  have  saved  the  town  half-an- 
hour's  darkness. 

Large  telegraph  offices  are  fitted  with  secondary  batteries. 
Many  motorists  owe  the  ignition  which  keeps  their  engines 
at  work  to  secondary  batteries.  It  is  secondary  batteries 
which  keep  the  wireless  apparatus  at  work  on  a  wrecked 
vessel  after  the  engines  have  stopped.  Indeed  secondary 
batteries  are  one  of  the  most  beneficent  inventions.  And 
if  only  they  could  be  made  in  a  lighter  form  than  is  possible 
at  present  their  value  would  be  infinitely  increased. 

We  have  seen  how  the  passage  of  current  through  acidu- 
lated water  produces  hydrogen  and  oxygen.  If  those  gases 
be  collected  in  closed  vessels  over  the  water,  so  that  they 
remain  in  contact  with  the  water,  as  soon  as  the  current  is 
stopped  a  reverse  action  sets  in.  The  gases  tend  to  re- 
combine  with  the  electrolyte  and  in  so  doing  to  give  back 
a  current  equal  to  that  which  formed  them.  Fig.  4  shows 
the  construction  of  what  is  called  a  voltameter,  in  which 
the  gases  arising  from  the  electrodes  are  collected  in  little 
glass  vessels  placed  just  above  them.  Such  an  apparatus 
enables  us  to  see  easily  how  the  accumulator  works.  The 
picture  shows  the  battery  which  is  effecting  the  separation 
of  the  oxygen  and  hydrogen.  If  that  be  disconnected,  and 
the  wires  joined,  as  shown  by  the  dotted  line,  a  current  will 
flow  back  until  the  oxygen  and  hydrogen  have  returned 
into  the  solution  again.  The  apparatus  will,  in  fact,  work 
like  an  ordinary  battery,  except  that  instead  of  a  plate  or 
rod  of  zinc  a  mass  of  hydrogen  will  form  the  essential  part. 

An  appliance  such  as  a  voltameter  is  not  of  much  use  for 
the  practical  purpose  of  storing  large  quantities  of  electrical 


64  SOME  VALUABLE  ELECTRICAL  PROCESSES 

energy,  because  the  surfaces  of  the  electrodes  are  so  small 
and  the  surfaces  where  liquid  and  gases  are  in  contact  are 
small  too.  It  is  clear  that  the  larger  the  electrodes  are  the 
wider  will  be  the  passage  for  the  current,  just  as  a  wide  road 
can  accommodate  more  traffic  than  a  narrow  path.  We 
may  regard  the  electrodes  as  like  gateways  through  which 
the  current  passes.  By  making  them  large,  therefore,  we 


ft  cilfSf  t.  /«  Sect 

FIG.  4 

enable  a  large  current  to  pass,  and  consequently  permit 
electrolysis  to  take  place  with  great  comparative  rapidity. 

The  "  plates,"  as  the  electrodes  in  a  secondary  battery  are 
termed,  are  generally  large  metal  plates.  Experiment  has 
shown  that  lead  is  the  best  for  this  purpose.  It  has  also 
been  found  that  it  can  be  improved  by  making  it  porous, 
since  the  inner  surfaces  of  the  pores  are  so  much  added 
surface  through  which  current  can  pass  into  the  electrolyte. 
There  are  various  ways  of  producing  this  porosity,  which 
need  not  trouble  us  here,  however.  It  will  suffice  for  our 
purpose  to  understand  that  an  ordinary  secondary  cell 
consists  of  two  lead  plates,  with  the  largest  possible  surface, 
immersed  in  a  liquid,  generally  a  dilute  solution  of  sulphuric 
acid  in  water. 

To  charge  the  battery,  current  is  sent  to  one  plate,  through 
the  liquid  to  the  other  plate,  and  so  away.  A  thin  film  of 
hydrogen  is  thus  formed  upon  the  outgoing  plate,  while 
oxygen  is  formed  at  the  incoming  one.  Since  the  hydrogen 
is  spread  over  such  a  large  area,  it  does  not  accumulate 


SOME  VALUABLE  ELECTRICAL  PROCESSES  65 

sufficiently  for  much  of  it  to  rise  to  the  surface.  Most  of  it 
remains  adhering  to  the  plate.  The  oxygen  combines  with 
the  lead  of  its  plate  and  so  is  safely  stored  up  there  in  the 
form  of  oxide  of  lead.  This  storage  of  hydrogen  upon  the 
one  plate  and  oxygen  on  the  other  cannot  go  on  indefinitely, 
and  so  as  soon  as  the  limit  is  reached  the  cell  is  fully  charged. 
Passage  of  further  current  is  then  simply  waste. 

The  dynamo  or  primary  batteries  which  are  used  for 
charging  having  been  disconnected,  the  two  plates  can  be 
connected  together  through  lamps,  motors,  or  in  any  other 
desired  way,  and  the  current  will  then  flow  out  again,  the 
opposite  way  to  that  in  which  it  entered,  just  as  a  stone 
thrown  up  in  the  air  returns  the  opposite  way.  The  current 
which  comes  out  is,  in  fact,  a  sort  of  reflex  action  arising 
from  that  which  went  in,  the  mechanism  by  which  it  is 
produced  being  the  reabsorption  of  the  oxygen  and  hydrogen 
into  the  electrolyte. 

Whether  a  cell  is  fully  charged  or  not  is  ascertained  by 
weighing  the  electrolyte,  an  operation  which  at  first  sight 
seems  to  have  nothing  whatever  to  do  with  the  matter.  It 
arises  from  the  difference  in  weight  between  water  and 
sulphuric  acid,  the  latter  being  the  heavier.  We  have  seen 
that  while  a  little  acid  must  be  added  to  water  before  it 
can  be  electrolysed,  it  is  the  water  which  is  ultimately 
resolved  into  its  constituent  gases.  Hence  the  result  of 
electrolysis  is  to  increase  not  the  amount,  but  the  proportion 
of  acid.  Therefore  it  increases  the  weight  of  the  electrolyte. 
This  weight  is  ascertained  by  means  of  a  "  hydrometer," 
a  glass  tube,  stopped,  and  loaded  with  some  small  shot  at 
its  lower  end.  On  the  upper  part  is  engraved  a  graduated 
scale,  so  that  the  exact  depth  to  which  it  sinks  can  be  easily 
read.  This  depth  will,  of  course,  vary  with  the  specific 
gravity  of  the  liquid,  and  so  the  depth  recorded  by  the  scale 
will  be  an  indication  of  the  proportion  of  acid,  and  that  in 
turn  will  show  how  far  the  process  of  charging  has  progressed. 

Accumulators  are,  or  have  been  hitherto  at  any  rate,  very 
troublesome  things.  They  are  apt  to  lose  their  power.  If 

£ 


66  SOME  VALUABLE  ELECTRICAL  PROCESSES 

not  properly  charged  they  are  easily  damaged.  Too  rapid 
charging  or  too  rapid  discharging,  standing  for  a  while  only 
partly  charged — all  these  things  have  a  bad  effect,  in  extreme 
cases  even  destroying  them  altogether.  Because  of  the  use 
of  lead  they  are  terribly  heavy  too,  so  much  so  that  for 
traction  purposes  they  are  of  very  little  use,  for  a  large 
amount  of  the  energy  stored  in  the  accumulators  is  then 
used  up  in  hauling  them  about. 

Yet  what  a  field  there  is  for  the  successful  accumulator  ! 
Take  the  one  instance  of  the  electrification  of  a  railway.  If 
good  light  and  efficient  accumulators  were  to  be  had,  no 
alteration  at  all  would  be  necessary  to  the  permanent  way. 
The  engines  or  motor  carriages  would  need  to  go  periodically 
to  a  depot  to  be  re-charged,  but  that  could  easily  be  arranged. 
Such  things  as  conductor  rails,  overhead  conductors  and 
so  on  would  be  needless. 

The  world  has  therefore  been  interested  for  years  in  the 
rumour  that  T.  A.  Edison  was  engaged  upon  this  problem, 
and  at  last  he  has  produced  his  accumulator,  by  which  he 
has  removed  many  of  the  difficulties,  if  not  all.  Instead  of 
a  case  of  glass  or  celluloid,  as  is  usual  with  the  older  cells, 
his  cells  are  enclosed  in  strong  boxes  of  nickel  steel.  The 
positive  plate  consists  of  nickel  tubes  filled  with  alternate 
layers  of  nickel  hydroxide,  while  the  negative  plate  is 
formed  of  prepared  oxide  of  iron  in  a  nickel  framework. 
The  electrolyte  is  a  solution  of  potassium  hydroxide.  The 
chemical  action  and  the  electrical  reaction  is,  of  course,  on 
the  same  principle  precisely  as  in  the  older  cells,  but  it  is 
claimed  that  the  Edison  cells  are  "  fool-proof" — that  is  to 
say,  they  cannot  be  damaged  by  careless  handling,  and  they 
appear  to  be  a  little  lighter.  Thus  the  problem  is  partly 
solved,  and  with  that  as  a  fresh  starting-point  someone  may 
sooner  or  later  give  us  a  secondary  battery  which  is  light  as 
well  as  strong. 

If  any  would-be  scientific  inventor  reads  these  words 
there  is  a  suggestion  for  a  promising  line  of  investigation. 


CHAPTER  V 

MACHINE-MADE  COLD 

ONE  of  the  most  remarkable  adaptations  of  scientific 
knowledge  is  the  "  manufacture  of  cold."  At  first 
that  phrase  seems  strange,  but  it  is  really  quite 
legitimate.  There  are  machines  at  work  at  this  moment 
which  are  turning  out  cold  as  if  it  were  any  other  manu- 
factured article.  It  is  not  that  they  manufacture  cold 
water  or  cold  air,  it  is  the  cold  itself  which  they  produce. 

Of  course,  cold  has  no  real  existence,  since  it  is  simply  a 
negative  quantity,  an  absence  of  heat,  yet  its  effects  are 
so  real  that  we  are  in  the  habit  of  talking  of  it  as  if  it  were 
a  reality,  and  in  that  sense  we  can  regard  it  as  a  product 
of  manufacture. 

Moreover,  we  see  in  this  a  conspicuous  instance  of  the 
interdependence  of  invention  and  science,  for  scientific 
principles  were  first  adapted  to  produce  cold,  and  then 
artificial  cold  was  employed  in  scientific  investigations, 
whereby  the  rare  gases  of  the  atmosphere  have  been 
discovered,  as  we  shall  see  presently. 

In  Mechanical  Inventions  of  To-day  I  have  dealt  with  the 
uses  which  can  be  made  of  heat  as  a  motive  power.  Here 
we  have  in  some  sense  a  reversal  of  the  process.  In  the 
heat-engine  the  expenditure  of  heat  produces  motion.  In 
the  refrigerating  machine  motion  produces  heat,  on  the  face 
of  it  a  strange  way  of  producing  cold.  Yet  it  is  by  the 
production  of  heat  in  the  first  instance  that  we  are  ultimately 
able  to  obtain  the  cold. 

One  way  to  make  a  thing  cold  is  to  place  it  in  contact  with 
ice.  But  that  process  suffers  from  severe  limitations.  In 
the  first  place,  we  may  not  be  able  to  procure  ice  when  we 

67 


68  MACHINE-MADE  COLD 

want  it.    And  in  the  second  place,  we  may  want  to  produce 
a  temperature  much  lower  than  that  of  ice. 

Now  a  machine  can  produce  any  degree  of  coldness,  almost 
down  to  the  "  absolute  zero,"  the  point  at  which  a  body  is 
absolutely  devoid  of  any  heat  whatever,  the  condition  in 
which  its  molecules  are  absolutely  still.  That  point  is 
274°  C.  below  freezing-point.  Freezing-point  on  that  scale  is 
"zero,"  and  so  this  absolute  zero  is  minus  274°.  Or,  to  put 
it  another  way,  freezing-point  is  274°  absolute  temperature. 
The  absolute  zero  has  never  been  reached,  and  there  is 
reason  to  believe  that  it  never  can  be  quite  reached,  but 
by  methods  about  to  be  described  a  temperature  within 
a  few  degrees  of  it  has  been  attained.  And  all  of  this  can 
be  done  without  any  cooling  agent  colder  than  water  at  an 
ordinary  temperature. 

There  are  several  systems,  but  the  one  which  illustrates 
the  principle  most  simply  is  that  in  which  carbonic  acid 
gas  is  the  "  working  fluid."  This  is  a  very  compressible 
gas,  and  so  is  well  fitted  for  the  purpose.  First  of  all  a 
pump  or  compressor  compresses  it.  That  has  the  effect  of 
heating  it.  Such  we  might  expect  from  the  fact  that  heat 
is  molecular  activity  :  when  by  compressing  the  gas  we 
force  the  molecules  closer  together,  they  naturally  hit  each 
other  and  the  sides  of  the  containing  vessel  harder  than  they 
did  before,  and  the  increased  activity  is  manifested  as 
increased  heat.  So  the  first  effect,  as  was  remarked  just 
now,  is  to  produce,  apparently,  increased  heat. 

But  then  the  hot  compressed  gas,  by  being  passed  through 
a  coir  of  pipe  surrounded  by  cold  water,  can  be  robbed  of 
that  heat.  According  to  the  speed  at  which  it  traverses  the 
coil  it  will  be  more  or  less  cooled  :  by  causing  it  to  travel 
slowly  it  can  be  brought  down  almost  to  the  temperature 
of  the  water.  So  we  start  with  the  gas  at  atmospheric 
pressure  and  at  somewhere  about  atmospheric  temperature 
too.  This  we  convert  into  compressed  gas  at  a  high  tempera- 
ture. After  cooling  it  we  have  compressed  gas  at  a  moderate 
temperature. 


MACHINE-MADE  COLD  69 

Then,  to  complete  the  process,  we  let  the  gas  expand  again. 
Now  just  as  compressing  a  gas  heats  it,  letting  it  expand  cools 
it.  If  we  compressed  it  and  then  expanded  it  again  we 
should  be  just  as  we  were  to  commence  with.  But  since, 
in  between  the  two  operations  we  extract  a  quantity  of 
heat  by  means  of  the  cooling  water,  we  get  at  the  end  a 
very  much  lower  temperature  than  that  with  which  we 
started. 

We  cannot  cool  the  gas  without  compressing  it,  because 
heat  will  only  flow  from  one  body  into  another  when  the 
second  is  cooler  than  the  first.  But  by  making  the  gas  hot 
temporarily  by  compression  we  enable  the  water  to  draw 
some  heat  from  it,  and  then,  allowing  it  to  sink  back  to  its 
original  state,  we  get  practically  the  old  temperature,  less 
what  the  water  has  extracted.  The  principle  is  really 
absurdly  simple  when  one  once  gets  to  understand  it.  The 
application  is  not  so  simple  as  far  as  the  designer  of  the 
machine  is  concerned,  for  he  has  to  adjust  the  various  parts 
to  exactly  the  right  shape  and  dimensions,  so  that  they 
may  work  well  with  one  another  and  produce  the  desired 
result  with  the  minimum  expenditure  of  power. 

To  the  observer,  however,  and  to  the  user  too,  the  finished 
machine  is  wonderful  in  its  simplicity.  The  principle  is 
illustrated  diagrammatically  in  Fig.  5. 

In  the  centre  is  the  compressor.  Its  action  forces  the  gas 
along  the  pipe  to  the  right  and  down  into  the  condenser. 
As  it  flows  downwards  through  the  coil  there  cold  water 
enters  at  the  bottom  of  the  tank,  flows  upward  past  the  coil 
and  escapes  again  at  the  top.  Thus  the  coil  is  kept  in  contact 
with  cold  water. 

Passing  then  through  the  bottom  of  the  tank  the  gas 
travels  from  right  to  left  through  the  "  regulating  valve  " 
and  into  an  arrangement  almost  exactly  similar  to  the  con- 
denser but  called  the  evaporator.  Here  the  gas  expands 
and  suffers  a  great  fall  in  temperature.  This  cold  is  com- 
municated to  liquid  circulating  in  the  tank  which  forms  a 
part  of  the  evaporator,  and  this  liquid  can  be  circulated 


70 


MACHINE-MADE  COLD 


through  pipes  into  any  rooms  to  be  cooled  or  around  vessels 
of  water  which  it  is  desired  to  freeze.  This  liquid,  which 
acts  as  the  carrier  of  the  cold,  is  called  "  brine,"  and  is 
water  to  which  is  added  calcium  chloride  to  keep  it  from 
freezing. 

Now  the  observant  reader  may  have  noticed  that  there 
is  no  apparent  reason  for  the  name  of  the  left-hand  vessel. 
It  will  be  quite  clear,  however,  when  I  explain  that  although 


PIG.  5.— This  diagram  shows  the  working  of  the  Refrigerating  Machine.  The  pump 
compresses  the  gas  and  drives  it  through  the  coil  in  the  condenser,  where  it  is  cooled 
by  water.  It  passes  thence  through  the  coil  in  the  evaporator,  where  it  expands  and 
cools  the  surrounding  brine. 

I  have  spoken  of  the  working  fluid  all  along  as  gas,  I  have 
only  done  so  to  avoid  bringing  in  too  many  explanations  at 
once.  It  is  actually  liquid  for  a  good  part  of  its  journey. 
Carbonic  acid  gas  liquefies  at  a  very  moderate  temperature 
and  pressure,  and  so  while  it  leaves  the  compressor  as  a  gas 
it  becomes  liquid  in  the  condenser  and  remains  so  until  it 
has  passed  the  regulating  valve.  Then  it  begins  to  expand 
into  gas  once  more,  and  in  that  state  it  passes  back  to  the 
compressor. 

There  is  a  pressure-gauge  on  the  pipe  leaving  the  com- 
pressor and  another  on  the  one  entering  it.  A  comparison 
of  the  readings  on  these  two  tells  how  the  apparatus  is 


MACHINE-MADE  COLD  71 

working.  The  difference  between  them  indicates  how  much 
compression  is  being  given  to  the  gas.  Assuming  that  the 
compressor  is  working  at  a  constant  speed,  this  compression 
can  be  regulated  to  a  nicety  by  the  valve :  close  it  a  little 
and  the  compression  will  increase  :  open  it  a  little  and  the 
compression  will  decrease.  By  this  means  the  degree  of 
cold  produced  can  be  varied  at  will. 

This  is  the  way  in  which  many  ships  are  enabled  to  carry- 
cargoes  of  frozen  meat.  The  chambers  in  which  the  meat 
is  stowed  are  insulated — that  is  to  say,  their  walls  are  made 
as  impervious  as  possible  to  heat.  Then  the  brine  is  carried 
into  the  chambers  in  pipes,  cooling  them  much  as  the  hot- 
water  pipes  heat  an  ordinary  public  building. 

Or  another  method  is  to  carry  the  pipe  which  constitutes 
the  evaporator  into  the  chamber  to  be  cooled.  A  third 
way  is  to  dispense  with  brine  and  to  blow  air  through  the 
coils  of  the  evaporator,  whereby  the  air  is  made  to  carry 
away  the  cold  to  wherever  it  is  needed. 

Ice  can  be  made  easily  in  moulds  of  metal  or  wood  around 
which  brine  circulates.  If  made  of  ordinary  water  the  ice 
is  likely  to  be  cloudy  and  opaque,  which  is  quite  good  enough 
for  many  purposes.  In  cases  where  it  is  desired  that  it 
should  be  clear,  the  water  is  agitated  during  freezing,  or  else 
distilled  water  is  used.  To  enable  the  blocks  to  be  got  out 
of  the  moulds  it  is  sometimes  arranged  to  circulate  warm 
brine  for  a  few  moments. 

Ice  skating  rinks  are  formed  by  making,  first,  an  insulating 
layer  of  sawdust,  slag-wool  or  something  of  that  sort  (those 
by  the  way,  being  the  materials  generally  used  for  insulating 
cold  chambers)  underneath  the  floor.  The  floor,  too,  is 
made  waterproof  and  then  upon  it  is  laid  as  closely  as 
possible  a  series  of  iron  pipes.  Water  is  flooded  on  to  the 
floor  until  the  pipes  are  covered  to  a  depth  of  several  inches, 
and  then  brine  is  pumped  through  the  pipes.  In  time  the 
water  freezes,  and  so  long  as  the  brine  circulates  it  remains 
so. 

But  although  the  "  CO2  process  "  described  above  is  the 


72  MACHINE-MADE  COLD 

simplest  illustration  of  the  principle,  there  are  other  systems. 
In  one  very  popular  form  ammonia  gas  is  the  "  working 
fluid."  This  is  liquefied  by  pressure  and  cooling  with  water, 
being  subsequently  expanded  just  as  described  above. 

Another  much -used  system  is  the  "  ammonia-absorption  " 
process,  in  which  the  ammonia  is  not  liquefied,  but  when 
under  pressure  is  absorbed  by  water,  returning  to  gas  again 
when  the  pressure  is  released. 

But  the  degree  of  cold  attained  in  these  commercial 
machines  is  as  nothing  to  the  extremely  intense  cold  gener- 
ated on  the  same  principles  in  the  liquid-air  machine,  which 
is  found  in  every  well-equipped  physical  laboratory. 

Briefly,  this  consists  of  a  coil  of  many  turns  of  small 
tube  enclosed  in  a  small  double  vessel,  the  space  between 
the  inner  and  outer  skins  of  which  is  packed  with  insulating 
material.  A  compressor  pumps  air  in  at  the  top  of  the 
coil  at  a  pressure  of  from  150  to  200  atmospheres.  An 
"  atmosphere,"  it  may  be  remarked,  is  a  unit  often  used  in 
scientific  matters,  meaning  the  normal  pressure  of  the  atmos- 
phere, which  is,  roughly  speaking,  15  Ib.  per  square  inch. 
Hence  200  atmospheres  is  about  3000  Ib.  per  square  inch. 

Of  course  air  so  highly  compressed  as  that  is  hot,  but 
after  it  has  passed  down  the  coil  and  has  escaped  from  the 
valve  which  liberates  it  at  the  bottom  it  is  much  cooler. 
But  that  is  only  the  beginning  of  the  operation.  The 
expanded,  and  therefore  cooled,  air  finds  its  way  upward 
through  the  turns  of  the  coil  down  which  the  following  air 
is  coming.  That,  expanding  in  its  turn,  is  colder  still, 
because  of  the  cooling  action  of  the  first  air,  and  so  the 
process  goes  on. 

This  is  perhaps  easier  to  understand  if  we  imagine  that 
the  air  comes  through  the  coil  in  gusts  and  we  notice  what 
happens  to  each  succeeding  gust.  The  first  comes  down, 
expands,  cools  and  ascends,  thereby  cooling  the  second  gust 
as  it  comes  down.  The  second  then,  after  expansion,  will 
be  cooler  than  the  first  was.  That  in  its  turn  will  cool  the 
third,  and  so  the  third  after  expansion  will  be  cooler  than 


By  permission  of 


Messrs.  J.  and  E.  Hall,  Ltd.,  London  and  Dartford 

MACHINE-MADE  ICE 


Here  we  see  a  huge  block  of  ice  being  lifted  (it  may  be  on  a  hot  summer  day) 
from  the  mould  in  which  it  has  been  made 


MACHINE-MADE  COLD  73 

the  second.  And  that  will  go  on,  each  succeeding  gust  being 
cooler  than  the  one  before.  And  although  the  flow  of  air 
is  continuous,  and  not  in  gusts,  the  result  is  just  the  same  : 
it  goes  on  getting  cooler  and  cooler  until  at  last  the  air  comes 
out  in  its  liquid  form.  This  liquid  collects  in  a  little  chamber 
formed  at  the  bottom  of  the  vessel  which  contains  the  coil 
and  can  be  drawn  off  when  desired. 

Air  in  its  liquid  state  looks  very  much  like  water.  In 
fact  it  is  difficult  to  get  chance  observers  to  believe  that  it 
is  not  water.  It  boils  at  a  temperature  far  below  the  freezing- 
point  of  water,  so  that  liquid  air  if  placed  in  a  cup  made  of 
ice  will  boil  furiously.  Ice  is  so  much  the  hotter  that  it 
behaves  towards  liquid  air  as  a  very  hot  fire  does  to  water. 

The  feature  of  the  above  machine,  it  will  be  noticed,  is 
that  no  cooling  water  is  required,  as  in  the  refrigerating 
machine,  although  the  principle  of  the  two  is  the  same. 
The  coil  is  the  "  condenser  "  and  the  vessel  in  which  it  is 
enclosed  is  the  "  evaporator,"  and  so  the  cold  air  produced 
by  the  process  in  the  evaporator  cools  the  coil  of  the  con- 
denser. Thus  it  is  "  self-intensive,"  as  the  makers  call  it. 

Hydrogen  can  be  liquefied  in  a  similar  machine,  except 
that  it  needs  a  little  preliminary  cooling  with  liquid  air. 
Liquid  hydrogen  is  the  coolest  thing  known  approaching 
the  region  of  absolute  zero. 

And  now  we  can  turn  to  the  wonderful  discoveries  which 
have  followed  upon  the  manufacture  of  liquid  air. 

To  make  the  story  complete  we  need  to  go  back  to  the 
time  of  Priestly  and  Cavendish,  early  in  last  century.  They 
investigated  the  atmosphere  and  showed  that  it  consisted 
of  oxygen  and  nitrogen  in  certain  invariable  proportions, 
with  under  certain  conditions  a  small  proportion  of  carbonic 
acid.  These  facts  were  so  well  authenticated,  and  they 
seemed  to  explain  everything  so  satisfactorily,  that  it  was 
quite  thought  almost  up  to  the  end  of  the  nineteenth  century 
that  there  was  nothing  more  to  learn  about  the  atmosphere. 

Nevertheless  there  was  an  idea  in  the  minds  of  some 
scientists  that  there  must  be  another  group  of  elements 


74  MACHINE-MADE  COLD 

somewhere,  the  existence  of  which  was  then  undiscovered, 
but  it  was  never  dreamed  that  these  were  in  the  air. 

Soon  after  the  weights  of  the  atoms  had  been  found  a 
medical  student  named  Prout  in  an  anonymous  essay  called 
attention  to  the  fact  that  there  were  curious  numerical 
relationships  between  them.  Speculation  on  the  subject 
went  on  for  many  years,  until  in  1865  the  great  Russian 
chemist  Mendeleeff  published  his  conclusions.  He  had 
arranged  the  elements  in  the  form  of  a  table  in  the  order  of 
their  atomic  weights.  The  table  consisted  of  twelve  rows  of 
names  forming  eight  vertical  columns,  and  the  remarkable 
thing  was  that  all  those  elements  which  fell  into  any  par- 
ticular column,  although  their  atomic  weights  were  very 
widely  different,  had  similar  properties.  This  enabled  him 
to  predict  the  discovery  of  certain  new  elements,  for  the  table 
contained  a  number  of  blank  spaces.  Three  elements  have 
been  found  since,  and  their  atomic  weights  and  properties 
are  just  such  as  to  fill  three  of  the  blank  spaces.  One  blank 
space,  it  is  thought,  may  be  filled  some  day  by  the  gas 
coronium,  which  like  helium  has  been  discovered  in  the  sun, 
but  unlike  it  has  not  yet  been  detected  here.  When  it  is, 
there  is  the  place  in  the  table  which  it  may  fill.  The  table 
then  commenced  with  what  is  still  called  Group  1,  but  for 
reasons  too  complicated  to  explain  here  it  appeared  as  if 
there  must  be  a  group  before  that,  a  group  the  chief  char- 
acteristic of  which  would  be  the  inactivity  of  the  elements 
included  in  it.  These  were  expected  to  be  of  various  atomic 
weights,  but  these  weights,  it  was  anticipated,  would  so 
occur  in  the  intervals  between  the  others  that  they  would 
all  fall  into  a  new  column  to  the  left  of  "  Group  1." 

In  the  year  1892  Lord  Rayleigh  was  investigating  the 
question  of  the  density  of  a  number  of  different  gases,  in- 
cluding, so  it  happened,  nitrogen.  Now  there  are  several 
ways  of  procuring  nitrogen.  One  is  to  get  it  from  the 
atmosphere  by  ridding  it  of  the  oxygen  with  which  it  is 
normally  mixed.  Another  way  is  to  split  up  some  com- 
pound, such  as  ammonia,  of  which  it  forms  a  part,  in  such  a 


MACHINE-MADE  COLD  75 

way  as  to  catch  the  nitrogen  and  leave  the  other  elements 
with  which  it  was  combined  elsewhere. 

Lord  Rayleigh  tried  both  ways,  and  he  found  that  the 
nitrogen  from  the  atmosphere  was  denser  than  that  derived 
from  ammonia.  Sir  William  Ramsey  then  carried  the 
matter  a  step  further.  He  heated  atmospheric  nitrogen  in 
the  presence  of  magnesium,  under  which  conditions  some 
of  the  nitrogen  combines  with  the  latter  element  to  form 
nitride  of  magnesium.  That,  it  was  found,  made  the  remain- 
ing nitrogen  denser  still.  The  explanation  then  seemed 
obvious.  Suppose  we  imagine  a  mixture  of  sawdust  and 
iron  filings :  it  will  be  heavier  than  an  equal  quantity  of 
pure  sawdust.  And  if  we  contrive  to  take  away  some 
of  the  sawdust  from  the  mixture  we  shall  find  that  what  is 
left  is  heavier  still,  when  compared  with  an  equal  bulk  of 
pure  sawdust.  For  it  is  clear  that  as  we  take  away  sawdust 
we  thereby  increase  the  proportion  of  the  heavier  iron  filings 
and  so  we  make  the  mixture  heavier. 

Applying  a  similar  process  of  reasoning  to  these  discoveries, 
the  conviction  grew  that  the  nitrogen  of  the  air  was  not  pure, 
but  that  it  had  mixed  with  it  a  small  proportion  of  some 
other  gas  of  greater  density.  They  soon  succeeded  in  isolat- 
ing this  denser  gas,  to  which  they  gave  the  name  of  argon. 
Its  atomic  weight  was  found,  and,  wonderful  to  relate,  it 
was  such  that  argon  fell  into  a  new  column  to  the  left  of 
Group  1,  as  had  been  anticipated. 

The  discovery  of  argon  was  announced  in  1894.  The  next 
year  Sir  William  Ramsey,  investigating  a  gas  which  had 
been  discovered  locked  up  in  the  interstices  of  a  mineral 
called  clevite,  was  able  to  state  that  it  was  helium,  the 
element  which  had  been  previously  noticed  by  the  spectro- 
scope in  the  sun.  Like  argon,  it  was  found  to  be  extremely 
inactive,  and  its  atomic  weight  turned  out  to  be  such  that 
it  too  fell  into  the  "  Zero  Group." 

In  1898  Professors  Ramsey  and  Travers  found  two  more 
gases  in  the  air,  krypton  and  neon,  and  a  little  later  still, 
there  was  found  mixed  with  the  krypton  a  further  new  gas, 


76  MACHINE-MADE  COLD 

xenon.    All  of  these  had  their  atomic  weights  found,  and 
fell  into  that  new  column  in  the  periodic  table. 

But  what  has  all  this  got  to  do  with  liquid  air  ?  The  two 
subjects  are  closely  related,  for  it  is  by  liquid-air  machines 
that  these  rare  gases  are  now  obtained,  and  it  was  from 
liquid  air  that  the  last  three  were  first  discovered. 

For  air,  as  we  well  know,  is  a  mixture  of  gases,  and  when 
extreme  cold  and  pressure  are  applied  these  gases  liquefy, 
each  behaving  according  to  its  own  nature.  They  do  not  all 
liquefy  at  the  same  time,  nor  on  being  relieved  from  the 
pressure  and  heated  do  all  evaporate  again  at  the  same 
temperature.  Although  they  emerge  from  the  liquid-air 
machine  in  the  form  of  a  single  liquid,  it  is  really  a  mixture 
of  liquids,  each  with  its  own  boiling-point. 

In  an  earlier  chapter  we  saw  how  petroleum  can  be  separ- 
ated into  its  various  constituents,  such  as  petrol,  by  fractional 
distillation,  advantage  being  taken  of  the  difference  in  the 
"  boiling-point  "  of  the  various  "  fractions."  The  boiling- 
point  of  a  liquid  is,  of  course,  the  temperature  at  which  it 
turns  freely  into  vapour,  and  just  as  petroleum  when  heated 
gives  off  first  cymogene,  next  rhigolene,  then  petrol,  benzine, 
kerosene  and  so  on,  in  the  order  named,  so  liquid  air,  when 
it  is  evaporated,  gives  off  its  different  constituents  in  order. 
Nitrogen,  oxygen,  argon,  helium,  krypton,  neon  and  xenon 
can  all  be  separated  each  from  the  others  in  this  way,  by 
"  fractional  distillation."  The  heat  from  the  surrounding 
objects  is  allowed  to  get  at  the  liquid,  and  the  gases  are 
then  given  off  in  the  order  of  their  boiling-points. 

And  thus  we  see  how  the  mechanical  production  of  cold 
has  assisted  in  the  pursuit  of  pure  science.  The  newly- 
found  gases  are  not  of  any  great  use  at  present.  They  are 
so  inactive  that  possibly  they  never  will  be,  with  one  excep- 
tion, and  that  is  neon.  If  an  electric  discharge  be  made 
to  pass  through  a  tube  filled  with  this  gas,  a  beautiful  glow 
is  the  result,  and  it  is  just  possible  that  neon  tubes  may 
become  the  electric  light  of  the  future.  That  is  only  a 
prediction,  however,  and  a  hesitating  one  at  that. 


MACHINE-MADE  COLD  77 

The  inactive  elements  may  become  of  value  in  explosives. 
We  have  seen  how  important  nitrogen  is  in  these  dangerous 
substances,  the  chief  feature  of  which  is  their  instability — 
their  readiness,  that  is,  to  change  into  something  else — which 
instability  is  due  to  the  reluctance  with  which  nitrogen 
enters  into  them.  Now  nitrogen,  though  inactive,  is  much 
less  so  than  these  others,  and  if  a  way  should  ever  be  found 
of  inducing  them  to  enter  into  a  compound,  that  compound 
will  probably  be  an  extremely  powerful  explosive. 


CHAPTER  VI 

SCIENTIFIC  INVENTIONS   AT  SEA 

THE  safety  of  our  fellow-creatures  has  always  been 
a  strong  stimulus  to  our  inventive  faculties.  The 
occurrence  of  a  bad  railway  accident,  and,  roughly, 
its  nature,  can  be  inferred  from  the  files  of  the  Patent  Office, 
for  such  an  event  brings  men's  thoughts  to  devising  ways 
and  means  of  preventing  a  recurrence,  and  an  avalanche  of 
such  inventions  descends  upon  the  patent  department  in 
consequence.  In  like  manner  a  particularly  distressing 
accident  to  a  lifeboat  some  years  ago  brought  out  many 
inventions  for  the  improvement  of  those  romantic  craft. 
Many  of  the  inventions  which  arise  under  these  conditions 
are,  of  course,  utterly  worthless,  but  some  of  them  "  come 
to  stay." 

It  is  not  surprising,  therefore,  when  we  think  of  the  almost 
innumerable  wrecks  which  happen,  even  with  modern 
shipping,  that  human  ingenuity  has  been  extremely  busy 
in  devising  ways  for  bringing  more  of  safety  and  less  of 
risk  into  the  lives  of  those  who  go  down  to  the  sea  in  ships. 
Of  these  perhaps  none  is  more  fascinating  than  the  modern 
lighthouse,  with  its  tall  tower,  its  brightly  flashing  light, 
standing  undisturbed  in  the  wildest  storm,  quietly  and 
persistently  sending  forth  its  guiding  rays,  no  matter  how 
the  elements  may  be  buffeting  it.  There  is  something 
specially  attractive  in  this  perfect  embodiment  of  quiet 
strength  and  devotion  to  duty. 

Of  course,  its  origin  is  very  ancient.  One  of  the  earliest 
inventions,  no  doubt,  was  the  bright  thought  of  a  very 
primitive  man  who  lit  a  fire  on  a  hill  to  serve  as  a  guide  to 
some  belated  friends  out  in  their  fishing  canoes.  From 

78 


SCIENTIFIC  INVENTIONS  AT  SEA  79 

some  such  beginning  the  modern  lighthouse,  a  magnificent 
product  of  the  science  of  civil  engineering  and  the  science 
of  optics,  has  arisen. 

Of  the  difficulties  encountered  in  the  construction  of 
lighthouse  towers  on  outlying  rocks  much  has  been  written. 
The  historic  Eddystone,  for  example,  has  quite  a  voluminous 
literature  of  its  own.  Of  the  light  itself,  however,  much 
less  is  known. 

It  will  be  interesting  first  to  note  the  different  purposes 
for  which  a  light  may  be  required,  and  then  see  how  the 
apparatus  of  the  lighthouse  is  made  to  serve  these  purposes. 

There  is  the  "  making  "  light,  perched,  if  possible,  upon 
some  high  eminence,  deriving  its  name  from  the  fact  that 
the  sailor  sights  it  as  he  is  "  making  "  the  land.  Vessels 
approaching  England  from  the  south-west  by  night  first 
see  the  light  at  the  Lizard.  The  transatlantic  vessels  know 
they  are  approaching  land  by  catching  sight  of  the  Fastnet 
Rock  light  off  the  coast  of  Ireland.  Cape  Race  light  serves 
in  the  same  way  for  those  about  to  enter  the  St  Lawrence 
and  Navesink  for  the  entrance  to  New  York  harbour.  All 
such  as  these  have  to  be  of  the  greatest  power  practicable, 
so  that  they  may  be  visible  not  only  at  the  longest  possible 
distance,  but  also  under  unfavourable  conditions,  such  as 
haze  and  slight  fog.  No  light,  of  course,  can  penetrate 
thick  fog,  but  in  light  fog  and  haze  a  powerful  light  can  be 
seen  at  considerable  distances.  For  the  same  reason  these 
lights  must  be  high  up,  or  the  curvature  of  the  ocean's 
surface  will  limit  their  range.  A  light  elevated  100  feet 
above  the  sea-level  wiH  be  visible  nearly  16  miles  away, 
but  if  only  50  feet  up  it  will  be  invisible  at  13  miles.  To  be 
seen  40  miles  away  it  must  be  as  high  as  1000  feet. 

But  then  again  height  is  in  some  cases  a  disadvantage, 
for  sometimes  fog  hovers  a  little  distance  above  the  sea, 
while  below  it  the  air  is  clear,  and  the  higher  a  light  may  be 
the  more  likely  is  it  to  have  its  lantern  immersed  in  a  floating 
cloud  of  fog.  Many  readers  familiar  with  the  south  coast 
of  Britain  will  remember  that  the  light  which  used  to  show 


80  SCIENTIFIC  INVENTIONS  AT    SEA 

on  the  summit  of  Beachy  Head  is  there  no  more,  but  has 
been  replaced  by  a  tower  at  the  foot  of  the  cliffs,  the  reason 
being  that  it  may  be  below  the  clouds  of  fog  which  are 
prevalent  at  that  point. 

But  the  mention  of  Beachy  Head  introduces  us  to  another 
class  of  lights,  known  as  "  coasting  "  lights,  since  they  are 
intended  to  lead  the  mariner  on  from  point  to  point  along 
a  coast.  It  will  be  seen  at  once  that  in  many  cases  they  do 
not  need  to  be  visible  at  such  great  distances  as  the  mak- 
ing lights.  When  the  mariner  has  sighted  the  Lizard,  for 
example,  he  knows  where  he  is.  In  order  that  he  may  learn 
that  important  fact  as  soon  as  possible  it  is  desirable  that 
that  light  should  have  the  greatest  possible  range,  but 
having  thus  located  himself,  when  he  begins  to  feel  his  way 
along  the  English  Channel  he  is  guided  by  the  coasting 
lights,  and  so  long  as  they  are  of  such  range  that  he  will 
never  be  out  of  sight  of  one  or  two  of  them  that  will  be 
sufficient.  Thus  the  Beachy  Head  light,  in  its  present  low 
position,  has  a  sufficient  range  for  its  purpose,  with  the  added 
advantage  of  more  freedom  from  obscuration  by  fog.  Thus 
we  see  how  the  local  conditions  and  the  purpose  of  each 
particular  light  have  to  be  taken  into  consideration  in 
determining  its  position  and  power. 

The  Eddystone,  again,  is  an  example  of  a  further  class. 
It  simply  serves  to  denote  the  position  of  a  group  of  dangerous 
rocks.  Its  function  is  not  so  much  guidance,  although  no 
doubt  it  often  serves  for  that,  but  for  warning.  The  Lizard 
light  beckons  the  on-coming  ship  to  the  safety  of  the  English 
Channel ;  the  Eddystone  warns  it  away  from  danger.  The 
latter,  therefore,  and  similar  lights  are  "  warning  "  lights. 

Right  at  the  entrance  to  the  English  Channel,  that  greatest 
of  all  highways  for  shipping,  there  lie  the  Scilly  Isles.  This 
group  comprises  some  few  islands  of  fair  size  from  which 
we  draw  those  plentiful  supplies  of  beautiful  spring  flowers, 
but  it  also  includes  a  large  number  of  rocky  islets  which  have 
sent  many  a  strong  ship  to  its  doom.  On  one  of  the  islets, 
therefore,  the  Bishop's  Rock,  there  now  stands  a  very 


o     « 

f-     -o 

o     § 


SCIENTIFIC  INVENTIONS  AT  SEA  81 

powerful  light  which  exemplifies  many  whose  purpose  is  the 
double  one  of  welcoming  the  mariner  as  he  approaches  our 
shores  and  at  the  same  time  warning  him  of  a  local  danger. 
Such  are  both  making  and  warning  lights. 

Of  no  less  importance,  though  less  impressive,  are  the 
guiding  lights,  which  guide  the  ships  into  and  out  of  harbours 
and  through  narrow  channels.  These  are  generally  arranged 
in  pairs,  one  of  the  pair  being  a  little  way  behind  and  above 
the  other.  Thus  when  the  sailor  sees  them  both,  one 
exactly  over  the  other,  he  knows  he  is  on  the  right  course. 

Sometimes  lighthouses  have  subsidiary  lights  as  well  as 
the  main  light,  to  mark  a  passage  between  two  dangers,  or 
to  give  warning  of  some  danger.  The  subsidiary  lights  are 
often  coloured,  and  they  are  generally  "  sectors  "  showing 
not  all  round  a  complete  circle,  or  even  a  considerable 
portion  of  one,  but  just  in  one  certain  direction.  They  are 
generally  shown  from  a  window  in  the  tower  lower  down 
below  the  main  light. 

Finally,  it  is  important  to  remember  that  every  light 
must  be  distinguishable  from  its  neighbours.  Hence  every 
one  in  any  given  locality  has  a  different  "  character  "  from 
all  the  others.  This  character  is  given  to  it  by  means  of 
flashes.  Instead  of  showing,  as  the  primitive  lights  did,  a 
steady  light,  the  modern  lighthouse  exhibits  a  series  of 
flashes,  the  duration  of  which,  together  with  the  intervals 
between,  give  it  its  distinctive  character.  This  flashing 
arrangement  has  a  further  advantage  over  the  steady  light. 
Each  flash  can  be  made  more  powerful  than  a  steady  light 
could  be.  But  of  that  more  later. 

The  actual  source  of  light  varies  with  circumstances. 
The  electric  arc  is,  as  we  all  know,  a  very  powerful  light, 
in  fact  it  can  be  made  the  most  powerful  of  all,  but  its  light 
is  decidedly  bluish.  Now  the  time  when  a  light  is  most 
of  all  needed  is  when  the  weather  is  thick.  Fogs  varying 
from  a  slight  haze  to  a  thick  pall  of  darkness  are  of  very 
common  occurrence,  and  the  lighthouse  light  must  be  able 
as  far  as  possible  to  penetrate  them. 


82  SCIENTIFIC  INVENTIONS  AT  SEA 

As  a  matter  of  fact  clean  fog,  such  as  one  gets  at  sea,  is 
not  by  any  means  opaque.  The  black  fogs  of  the  great 
cities  are  another  matter,  but  they  are  not  the  sort  which 
afflict  the  mariner.  On  a  foggy  day  in  the  open  country 
or  by  the  sea  it  is  often  particularly  light ;  indeed  the  light 
is  of  a  peculiarly  diffuse  nature  which  gives  a  nice  even 
illumination  to  everything.  Thus  we  see  that  fog  is  really 
transparent,  but  it  diffuses  the  light.  It  does  not  stop 
the  light  rays,  but  simply  bends  them  about  and  scatters 
them  in  all  directions.  Thus  we  can  see  nothing  through 
the  fog,  yet  a  flood  of  light  reaches  us  through  it.  In  its 
effect  it  is  like  that  "  crinkled  "  glass  which  is  often  used 
for  partitions  between  rooms,  which  lets  light  through,  but 
which  cannot  be  seen  through. 

We  see,  then,  that  the  effect  which  a  fog  produces  is 
mainly  to  refract  the  light  rays.  Each  little  drop  of 
water  (for  it  must  be  remembered  that  fog  is  myriads  of 
tiny  drops  of  liquid  ;  it  is  not  vapour)  acts  like  a  minute 
lens,  and  bends  the  rays  which  pass  through  it.  And  the 
more  blue  a  ray  is  the  more  it  is  bent.  On  the  contrary,  the 
more  red  it  is  the  less  is  it  bent.  When  a  beam  of  light  is 
analysed  in  the  spectroscope  the  red  rays  are  bent  least 
and  the  blue  rays  most,  so  that  the  red  rays  fall  at  one  end 
of  the  spectrum  and  the  blue  at  the  other. 

Now  we  only  see  a  thing  when  light  rays  proceeding  from 
every  part  of  it  fall  straight  (or  nearly  so)  upon  our  eyes. 
Consequently,  since  red  rays  are  bent  and  scattered  by  the 
fog  less  than  blue  rays  are,  a  red  light  will  be  more  easily 
seen  through  a  fog  than  a  blue  one.  It  might  seem  from 
this  that  a  red  glass  put  in  front  of  a  light  would  make  it 
better  for  this  purpose,  but  that  is  not  the  case,  for  the 
simple  reason  that  filtering  the  light  through  red  glass  does 
not  really  make  it  any  redder  than  it  was  before  :  it  simply 
makes  it  look  redder  by  extracting  from  the  original  light 
all  except  the  red.  But  a  source  of  light  which  is  naturally 
reddish  is  so  because  it  is  more  plentifully  endowed  with 
Ted  rays,  while  a  bluish  light  like  the  electric  arc  is  naturally 


SCIENTIFIC  INVENTIONS  AT  SEA  83 

deficient  in  red  rays.  Consequently  we  should  be  inclined 
to  expect  from  theory  that  the  electric  arc  would  not  be  a 
good  light  for  a  lighthouse,  since  it  would  lack  penetrating 
power  in  foggy  weather.  Some  readers  may  have  noticed 
themselves,  in  towns  where  electric  lights  and  gas  lamps  are 
in  use  near  each  other,  that  the  latter,  though  relatively 
feebler  under  normal  conditions,  seem  to  give  more  light  in 
fog.  And  experiments  show  that  this  is  really  the  case. 
So  although  there  are  some  lighthouses  with  electric  arc 
lights,  that  which  is  now  believed  to  be  the  best  is  an  oil 
lamp  of  special  design,  using  a  mantle  of  the  Welsbach  type. 

The  oil  is  stored  in  strong  steel  reservoirs  into  which  air 
is  pumped  by  means  of  a  pump  not  unlike  those  used 
to  inflate  bicycle  tyres.  By  this  means  a  pressure  is 
maintained  upon  the  oil  of  about  65  Ib.  per  square  inch. 
This  forces  the  oil  up  a  pipe  and  drives  it  in  a  jet  into  a 
vaporiser,  a  tube  heated  from  the  outside  so  that  in  it  the 
oil  is  turned  into  gas.  This  gas  then  rises  to  the  burner 
and  heats  the  mantle,  just  as  the  gas  does  in  the  ordinary 
incandescent  gas  light.  Indeed  in  the  case  of  lights  on 
the  mainland  near  a  town  the  gas  from  the  town  main  is 
often  utilised.  But  this  simple  arrangement  for  using 
vaporised  oil,  as  will  readily  be  seen,  can  be  employed 
anywhere.  A  little  of  the  gas  produced  is  led  through  a 
branch  pipe  and  burnt  to  heat  the  vaporiser.  To  start 
the  apparatus  the  vaporiser  is  heated  with  a  little  methylated 
spirit.  Thus  everything  is  quite  self-contained  and  so  simple 
that  there  is  little  to  get  out  of  order.  The  largest  size  of 
lamp  will  give  2400  candle-power,  with  an  expenditure  of 
2J  pints  of  oil  per  hour,  just  common  oil,  too,  of  the  kind 
used  with  ordinary  wick  lamps. 

Having  got  a  source  of  powerful  light,  the  next  thing  is 
to  collect  that  light  and  throw  it  in  the  direction  required. 
For  the  light  proceeds  from  the  lamp  in  all  directions  (practic- 
ally), and  much  of  it  would  be  entirely  wasted  could  it  not 
be  collected  and  guided  in  the  required  direction. 

The  earliest  attempt  at  this  was  to  use  a  reflector  of  bright 


84  SCIENTIFIC  INVENTIONS  AT  SEA 

polished  metal.  In  the  most  improved  form  these  were 
made  to  that  peculiar  curve  known  as  a  parabola.  This  is  a 
curve  obtained  by  cutting  a  cone  in  a  certain  way,  wherefore 
it  is  one  of  the  "  conic  sections,"  and  its  particular  appro- 
priateness for  this  work  resides  in  the  fact  that  if  a  light 
be  placed  at  a  certain  point  known  as  the  "  focus  "  all  the 
diverging  rays  which  fall  upon  the  reflector  will  be  reflected 
in  the  same  direction,  parallel  to  each  other.  An  ordinary 
spherical  mirror  would  reflect  them  either  back  to  the 
lamp  or  in  diverging  directions. 

At  any  distance  the  beam  from  the  parabolic  reflector 
will  be  more  intense  than  that  from  the  spherical  one,  since 
the  rays  will  be  closer  together.  But  even  with  the  parabolic 
one  there  is  some  diffusion,  for  the  simple  reason  that  whereas 
the  focus  is  a  mathematical  point  (position  without  magni- 
tude) the  most  concentrated  form  of  light  known  has  a 
considerable  magnitude.  Hence  the  rays  proceeding  from 
the  centre  of  the  mantle  are  reflected  as  per  the  theory,  but 
those  from  the  outlying  parts  of  it  are  somewhat  diffused. 
This  difficulty  cannot  possibly  be  overcome,  and  hence  even 
in  the  finest  examples  of  lighthouse  architecture  the  flashes 
are  not  quite  sharp  and  clear-cut.  There  is  a  central  moment, 
so  to  speak  wherein  the  flash  is  almost  blinding  in  its 
intensity,  but  it  is  preceded  by  a  period  of  growing 
brightness  and  succeeded  by  one  of  decreasing  light. 

In  the  modern  apparatus,  however,  metallic  mirrors  are 
entirely  dispensed  with,  their  place  being  taken  by  reflecting 
prisms  of  glass.  The  metallic  ones  had  to  be  continually 
rubbed  to  keep  them  clean,  and  this  soon  dulled  their  bright- 
ness, while  the  glass  prisms  need  only  to  be  wiped  carefully, 
which  operation  has  little  effect  upon  their  surface. 

It  may  come  as  a  surprise  to  some  that  reflecting  prisms 
are  possible.  The  idea  of  refraction  through  a  prism  is 
quite  familiar.  Such  forms  the  essential  principle  of  the 
spectroscope.  Refraction  is  explained  to  every  school  child 
in  order  to  account  for  the  rainbow.  But  reflection  by  a 
piece  of  the  clearest  glass  seems  a  contradiction  in  terms 


SCIENTIFIC  INVENTIONS  AT  SEA  85 

almost.  Yet  it  is  only  a  question  of  shape.  In  some  prisms 
the  light  is  simply  bent  as  it  passes  through.  In  others 
it  is  bent  twice,  so  that  it  leaves  the  prism  just  as  if  it  had 
been  reflected  off  a  mirror.  Both  devices  are  used  in  the 
lighthouse.  Let  us  see  how  they  are  combined  so  as  to 
perform  the  work  to  be  done. 

Take  first  of  all  the  case  of  a  light  upon  an  isolated  rock 
where  the  warning  is  needed  equally  all  round.  All  that  is 
necessary  here  is  to  pick  up  those  rays  which,  if  left  to  them- 
selves, would  fall  upon  the  water  near  the  foot  of  the  tower, 
and  those  which  would  waste  themselves  skywards,  and  then 
to  gather  all  the  rays  into  several  bundles  or  beams.  We 
will  suppose  a  simple  case  in  which  the  light  is  supposed 
to  give  flashes  at  regular  intervals. 

We  are  in  the  topmost  room  of  the  lighthouse,  the  lantern, 
as  it  is  called.  In  the  centre  there  stands  the  murette  or 
pedestal.  In  this  several  columns  support  a  circular 
platform  on  the  top  of  which  there  moves  what  we  might 
call  a  turntable,  which  in  turn  bears  a  frame  of  gun-metal 
into  which  are  fitted  a  maze  of  glass  bars  triangular  in  section 
and  curved  to  form  concentric  circles.  The  whole  structure, 
possibly,  is  of  great  size.  From  the  floor  to  the  platform 
is  as  high  as  an  ordinary  man.  Indeed  around  the  turn- 
table there  is  a  gallery  which  forms  a  roof  over  our  heads, 
so  that  it  is  only  after  mounting  some  iron  steps  on  to  this 
gallery  that  we  are  able  to  examine  the  glass  part. 

As  we  ascend  we  notice  that  the  walls  of  the  chamber  as 
far  up  as  the  gallery  are  formed  of  iron  plates,  while  above 
that  there  is  a  metal  framework  filled  in  with  glass  panes, 
and  above  all  a  dome-shaped  roof. 

Having  reached  the  platform  we  proceed  to  examine  the 
glass,  and  we  find  that  the  metal  framework  forms  a  cage 
with  four  sides,  each  approximately  flat,  but  really  slightly 
spherical.  Each  of  these  sides  is  called  a  "  panel."  In  the 
centre  of  each  is  a  lens.  Peeping  through  the  interstices 
between  the  prisms,  we  perceive  that  the  lamp  is  inside  this 
structure,  exactly  in  the  centre,  so  that  its  light  shines 


86  SCIENTIFIC  INVENTIONS  AT  SEA 

directly  through  the  central  lens  or  bull's  eye.  Around 
this  bull's-eye  are  many  circles  of  glass  bar,  forming  refracting 
prisms.  Around  this  again  are  more  bars  in  the  form  of 
segments,  which  together  form  circles,  some  being  refract- 
ing prisms  and  others  reflecting  prisms.  All  the  light  rays 
from  the  lamp  which  fall  on  any  one  prism  are  deflected, 
so  that  they  proceed  approximately  in  the  same  direction. 
Those  prisms  in  the  upper  part  lay  hold  of  the  rays  which 
would  otherwise  go  up  into  the  sky.  Those  at  the  bottom 
collect  those  which  would  fall  near  the  foot  of  the  tower. 
So  scarcely  any  are  lost.  But  for  the  fact  that  the  lamp 
itself  is  comparatively  large  and  not  a  theoretical  point, 
as  already  explained,  the  beam  from  this  panel  would  be 
perfectly  straight,  parallel,  and  of  uniform  density  every- 
where. As  it  is,  it  widens  slightly  as  it  proceeds,  but, 
practically  speaking,  we  might  call  it  a  solid  beam  of  light. 

Each  of  the  panels  sends  forth  such  a  beam,  so  that  they 
strike  out  in  four  directions  from  the  central  lamp  much  as 
four  spokes  from  the  hub  of  a  wheel. 

Then  descending  once  more  to  the  floor  from  which  we 
started,  we  see  that  among  the  columns  there  is  a  large 
clockwork  arrangement,  the  purpose  of  which  is  to  drive 
round  the  turntable  and  all  that  it  carries — in  the  language 
of  the  lighthouse  engineer  the  "  optical  apparatus  "  or,  more 
briefly,  "  the  apparatus."  And  as  this  turns  the  radiating 
beams  of  light  sweep  round  the  horizon  and  in  succession 
strike  into  the  eyes  of  any  mariner  who  may  be  within  range. 
Each  time  a  beam  strikes  him  he  sees  a  flash.  If  the 
apparatus  revolve  once  a  minute  he  will  see  four  flashes 
every  minute,  one  from  each  panel. 

Let  us  consider,  then,  the  advantages  of  this  wonderful 
mechanism,  with  its  cunning  arrangement  of  prisms.  It  is 
these  latter,  of  course,  which  are  the  important  thing.  The 
rest,  the  mechanical  portion,  is  simply  for  the  purpose  of 
holding  them  and  turning  them  at  the  proper  speed.  In 
the  first  place,  the  contrivance  gives  us  flashes  instead  of  a 
steady  light ;  it  gives  the  lighthouse  its  "  character."  Then 


SCIENTIFIC  INVENTIONS  AT  SEA  87 

again  it  enhances  the  brightness  of  the  light.  Instead  of 
shining  all  round,  the  light  is  concentrated  in  four  special 
directions,  and  the  light  which  would  be  wasted  upwards 
or  downwards  is  saved  and  brought  into  use. 

But  suppose  that  the  lighthouse  we  are  considering  be 
near  the  shore,  so  that  there  is  no  need  for  it  to  throw  any 
light  in  one — the  landward — direction.  Then  we  should 
see  inside  the  revolving  framework  with  its  prisms  a  fixed 
frame  with  reflecting  prisms  which  would  catch  any  rays 
going  from  the  lamp  in  the  direction  of  the  land  and  simply 
hurl  them,  as  it  were,  back  into  the  flame.  Thus  the 
intensity  of  the  flame  becomes  increased  by  those  rays 
thrown  back  which  would  else  have  been  wasted. 

Or  suppose  that  the  character  of  the  light  is  such  that  the 
flashes  have  to  be  at  irregular  intervals.  Then  the  frame- 
work, instead  of  being  symmetrically  four- sided,  would  be 
of  an  irregular  shape. 

And  that  brings  us  to  a  beautiful  feature  of  the  mechanism 
of  the  apparatus.  We  have  been  discussing  a  four-panel 
arrangement.  Suppose  that  we  were  to  reduce  it  to  three. 
Then,  since  all  the  light  would  be  concentrated  into  three 
beams  instead  of  four,  each  beam  would  be  more  intense. 
We  should  thereby  have  increased  the  range  of  our  apparatus 
without  any  increase  in  the  cost  of  oil — for  nothing,  as  it 
were.  But  to  get  the  same  namber  of  flashes  per  minute 
we  should  have  to  drive  it  round  so  much  the  faster.  But 
increased  speed  means  increased  burden  on  the  keepers 
who  have  to  wind  up  the  heavy  weights  which  operate  the 
clockwork.  So  there  is  a  limit  to  the  speed  which  can  be 
attained. 

But  if  friction  can  be  almost  eliminated  the  apparatus 
can  revolve  at  a  high  speed  without  throwing  undue  burden 
upon  the  men.  But  how  can  friction  thus  be  got  rid  of? 
Messrs  Chance  Bros.,  the  great  lighthouse  constructors,  of 
Birmingham,  have  done  it,  almost  entirely,  by  floating  the 
apparatus  on  mercury.  The  turntable  has  on  its  under  side 
a  large  ring  which  nearly  fits  a  cast-iron  trough  on  the  top 


88  SCIENTIFIC  INVENTIONS  AT  SEA 

of  the  pedestal.  In  this  trough  there  is  mercury,  so  that 
upon  the  liquid  metal  the  apparatus  floats  as  if  upon  a 
circular  raft.  The  table  with  its  lenses,  prisms  and  other 
fittings  may  weigh  six  or  seven  tons,  yet  it  can  be  pushed 
round  by  one  finger. 

The  various  sizes  of  optical  apparatus  are  known  as 
"  orders."  One  of  the  "  first  order  "  has  a  focal  distance 
of  920  millimetres.  This  means  that  there  is  that  distance 
between  the  centre  of  the  lamp  and  the  bull's-eye.  They 
descend  by  successive  stages  down  to  the  sixth  order,  with 
a  focal  distance  of  150  millimetres,  while  the  most  important 
lights  are  of  an  order  superior  even  to  the  so-called  "  first," 
termed  the  "  hyper-radial,"  the  focal  distance  of  which  is 
1330  millimetres. 

A  recent  example  of  a  hyper-radial  light  is  at  the  well- 
known  Cape  Race  in  Newfoundland.  It  revolves  once  every 
30  seconds,  giving  a  flash  of  3  seconds  every  7J  seconds. 
The  optical  apparatus  weighs  seven  tons. 

Most  lighthouses  are  fitted  with  fog  signals  of  some  kind 
which  have  a  distinctive  character  the  same  as  the  lights. 
Some  are  horns  blown  at  intervals  by  compressed  air  often 
obtained  from  a  special  air-pump  driven  by  an  oil-engine. 
Another  thing  is  to  let  off  detonators  at  stated  intervals. 
But  perhaps  the  most  interesting  of  all  is  the  submarine 
telephone.  The  trouble  with  audible  signals  is  that  they 
are  apt  to  vary  as  the  conditions  of  the  atmosphere  change. 
For,  strange  though  it  may  appear,  the  air  which  is  the 
natural  medium  by  which  sounds  are  carried  to  our  ears 
is  really  a  very  bad  substance  for  the  purpose.  Water  is 
much  superior.  A  swimmer  who  cares  to  try  the  experiment 
of  lying  upon  the  water  with  his  ears  immersed  while  a 
friend  beats  a  gong  under  the  water  some  distance  off  will  be 
astounded  at  the  result.  So  many  modern  ships  are  fitted 
with  under- water  ears,  waterproof  telephone  receivers,  really. 
One  is  fixed  each  side  of  the  vessel,  the  wires  from  them 
being  led  to  telephone  receivers  near  the  bridge.  Many 
lighthouses  and  lightships  in  like  manner  are  fitted  with 


fly  permission  of  Messrs.  Chance  Bros,  and  Co.,  Ltd.,  Birmingha 

DASSEN  ISLAND  LIGHTHOUSE,  CAPE  OF  GOOD  HOPE 

This  lighthouse,  80  feet  high,  is  built  of  cast-iron  plates,  bolted  together 


SCIENTIFIC  INVENTIONS  AT  SEA  89 

under-water  bells  which  can  be  rung  at  intervals.  The 
sounds  so  conveyed  through  the  water  are  always  the  same. 
Atmospheric  or  similar  changes  have  no  effect  upon  them. 
And,  moreover,  the  officer  can  tell  which  side  of  his  ship  the 
bell  is.  If  it  be  on  his  port-side  it  sounds  louder  in  his 
port  telephone,  and  vice  versa.  By  turning  his  ship  until  he 
hears  them  equally  he  knows  that  he  is  pointing  directly  to 
or  from  the  bell.  Thus  if  the  bell  belong  to  a  warning  light 
he  can  steer  confidently  right  away  from  the  danger  even  in 
the  thickest  fog. 

But  science  has  not  only  provided  the  mariner  with  lights 
of  marvellous  power  and  of  strange  distinctive  characters, 
and  reliable  sound-signals  for  foggy  weather,  it  has  also 
found  him  a  reliable  compass,  but  that  is  worthy  of  a  chapter 
to  itself. 


CHAPTER  VII 

THE   GYRO-COMPASS 

THE  magnetic  compass  has  been  for  ages  the  mariner's 
guide  over  the  trackless  waters.  In  cloudy  weather 
it  has  been  his  only  means  of  knowing  the  direction 
in  which  his  craft  was  heading.  Indeed,  it  is  not  too  much 
to  say  that  the  maritime  commerce  of  the  world  was  based 
upon  the  behaviour  of  that  little  piece  of  magnetised  steel. 

It  has  always,  however,  been  subject  to  certain  faults.  To 
commence  with,  it  points,  not  to  the  geographical  north,  but 
to  the  "  magnetic  pole,"  a  point  some  distance  from  the 
geographical  pole,  and  one,  moreover,  which  is  not  quite 
permanent.  The  fact  that  the  magnetic  pole  varies  its 
position  is  impressively  shown  by  the  fact  that  a  special 
department  at  Greenwich  Observatory  is  continually  em- 
ployed, by  the  aid  of  delicate  self-recording  instruments, 
watching  and  setting  down  its  fluctations.  And  the  premier 
observatory  of  the  world,  it  should  be  remembered,  exists 
primarily,  not  in  the  interests  of  pure  science,  but  as  a 
department  of  the  British  Admiralty  in  order  to  study 
matters  of  interest  to  navigation.  Thus  we  have  testimony 
to  the  importance  of  these  little  vagaries  on  the  part  of  the 
magnetic  compass. 

But  in  addition  to  these  inherent  faults  there  is  a  new 
source  of  error  in  the  magnetic  compass  which  man  has 
introduced  himself  by  making  his  ships  of  iron  instead  of 
wood.  Every  ship  of  the  present  day  is  a  huge  magnet.  A 
piece  of  iron  left  in  the  same  position  for  a  length  of  time 
becomes  polarised,  which  is  to  say  that  it  acquires  the 
properties  of  a  magnet;  and  two  magnets  always  exert 
an  influence  upon  each  other.  Consequently  the  ship, 

90 


THE  GYRO-COMPASS  91 

after  lying  for  perhaps  a  year  in  one  position,  during  the 
period  of  building,  becomes  itself  magnetic  and  interferes 
with  its  own  compass. 

Then,  again,  our  methods  of  ship  construction  aggravate 
this  trouble.  It  is  believed  that  every  molecule  of  iron 
is  itself  a  minute  magnet  with  a  north  and  south  pole  of  its 
own.  These  lying  in  confusion  in  the  mass  of  unmagnetised 
iron  neutralise  each  other,  so  that  the  mass,  taken  as  a 
whole,  does  not  exhibit  any  magnetic  power.  But  if  by 
some  means  the  whole  of  the  millions  of  millions  of  mole- 
cules can  be  set  the  same  way — with  all  their  north  poles 
in  one  direction,  and  their  south  poles  in  the  opposite 
direction — then  they  will  all  act  together.  Instead  of 
neutralising  each  other  they  will  then  help  each  other,  and 
under  those  conditions  the  mass  of  iron  will  possess  that 
peculiar  power  which  is  distinctive  of  a  magnet.  So  long 
as  a  piece  of  iron  is  left  in  the  same  position  the  magnetism 
of  the  earth  is  thus  acting  upon  the  molecules.  Just  as  it 
tends  to  place  the  compass  needle  north  and  south,  so  it 
does  with  every  molecule  in  the  iron  mass.  And  if,  while 
lying  still,  the  iron  be  hammered,  the  shaking  of  the  mole- 
cules due  to  the  hammering  loosens  them  as  it  were  and 
assists  the  earth's  power  in  pulling  them  into  position. 

One  has  only,  then,  to  watch  the  riveting  up  of  a  ship, 
and  to  see  the  vigorous  way  in  which  the  riveters  wield 
their  hammers,  to  realise  that  when  the  thousands  or  even 
millions  of  rivets  have  all  been  finished  the  material  of  that 
ship  will  have  had  the  very  best  possible  chance  of  becoming 
magnetic. 

To  make  matters  worse  still,  ships  are  often  loaded  with 
great  weights  of  iron  among  their  cargo.  That,  too,  may 
affect  the  compass.  On  warships  there  are  the  heavy  guns, 
each  weighing,  with  its  turret,  hundreds  of  tons,  and  they 
move,  so  that  their  effect  upon  the  compass  is  not  always 
the  same,  but  may  vary  from  time  to  time.  And  finally 
one  may  mention  the  electrical  machinery  in  a  modern  ship 
consisting  largely  of  powerful  magnets. 


92  THE  GYRO-COMPASS 

Altogether,  then,  it  is  not  surprising  that  the  old  magnetic 
compass  is  somewhat  unreliable.  It  has  to  be  coaxed  into 
doing  its  duty.  Pieces  of  iron  and  magnets  have  to  be 
disposed  about  it  to  counteract  these  disturbing  influences 
with  which  it  is  surrounded.  Before  a  voyage  experts  have 
to  come  on  board  to  adjust  the  compasses,  and  even  then 
there  is  reason  to  believe  that  the  instrument  sometimes 
plays  the  ship  false. 

It  is  not  to  be  wondered  at,  then,  that  the  naval  authorities 
in  particular  throughout  the  world  have  welcomed  the 
advent  of  a  new  compass  which  appears  to  possess  none  of 
these  drawbacks.  It  points  to  the  geographical  north,  to 
the  actual  pivot,  if  one  may  so  speak,  upon  which  the  earth 
turns.  It  is  non-magnetic,  so  that  the  presence  of  iron  or 
magnets  even  in  its  immediate  neighbourhood  has  little  or 
no  effect  upon  it.  On  the  other  hand,  it  has  to  be  driven 
by  a  current  of  electricity,  and  it  seems  just  possible  that  in 
some  great  crisis  it  might  fail,  although  every  provision  is 
made  for  alternative  sources  of  supply  in  case  of  one  failing, 
and  there  is  always  the  possibility  of  falling  back  upon  the 
old  magnetic  compass  should  the  new  one  go  wrong. 

In  principle  the  improved  compass  is,  like  its  older  brother, 
simplicity  itself.  The  latter  is  but  a  small  piece  of  iron 
magnetised  ;  the  former  is  nothing  more  than  a  spinning-top. 

It  is  rather  strange  that  although  the  spinning  object 
has  been  a  familiar  toy  for  years,  and  that,  moreover,  its 
behaviour  has  been  the  subject  of  investigation  by  some 
very  eminent  scientific  men,  it  is  only  of  recent  years  that 
its  principles  have  been  put  to  practical  use. 

Everyone  is  familiar  with  the  fact  that  a  round  block  of 
wood  will  support  itself  upon  a  comparatively  tall  peg  so 
long  as  it  is  rapidly  rotating.  And  that  is  but  one  of  the 
curious  things  which  a  rotating  body  will  do.  For  example, 
imagine  a  wheel  mounted  upon  an  axle  the  ends  of  which 
are  supported  inside  a  ring,  while  the  ring  again  is  supported 
on  pivots  between  the  two  prongs  of  a  fork,  the  fork  being 
free  to  swivel  round  in  a  socket.  The  wheel  is  then  free 


THE  GYRO-COMPASS  93 

to  move  in  any  direction.  Technically,  it  is  said  to  have 
"  three  degrees  of  freedom."  It  can  spin  round,  its  axle  can 
turn  over  and  over  with  the  pivoted  ring  inside  which  it  is 
fixed,  while  it  can  also  swing  round  and  round  as  the  fork 
turns  in  its  socket.  Assuming  that  the  joints  are  all  perfectly 
free,  that  the  pivots  move  in  their  sockets  with  perfect 
freedom — which,  of  course,  they  do  not — then  a  wheel  so 
mounted  could  move  in  any  direction  under  the  influence  of 
any  force  that  might  act  upon  it.  Now  a  wheel  so  mounted 
if  left  alone  remains  in  precisely  the*  same  position  so  long 
as  it  goes  on  rotating.  If  it  be  turning  sufficiently  quickly 
its  tendency  to  remain  will  be  strong  enough  to  overcome 
the  friction  of  any  ordinarily  well-made  instrument.  Con- 
sequently a  wheel  of  that  description  has  been  used  to 
demonstrate  the  rotation  of  the  earth,  it  remaining  still 
(except,  of  course,  for  its  rotating  movement)  while  the  earth 
has  moved  under  it. 

Could  we  entirely  eliminate  the  effects  of  friction  that 
might  be  used  as  a  compass,  for  it  could  be  set,  say  with  its 
axle  pointing  north  and  south,  at  the  commencement  of  the 
voyage,  and  it  would  remain  so  despite  all  the  evolutions 
through  which  the  ship  might  go. 

But  there  is  a  better  scheme  even  than  that,  based  upon 
the  peculiar  behaviour  of  a  revolving  wheel  when  it  has  only 
two  degrees  of  freedom.  Suppose  that  we  dispense  with 
the  ring  employed  in  the  previous  arrangement,  pivoting 
the  ends  of  the  axle  between  the  prongs  of  the  fork.  The 
wheel  is  then  free  to  rotate,  and  its  axle  can  slew  round 
through  a  complete  circle  by  the  turning  of  the  fork  in 
its  socket,  but  there  can  be  no  tilting  of  the  axle.  Being 
thus  deprived  of  one  of  its  movements  the  gyroscope  with 
three  degrees  becomes  a  gyroscope  with  two  degrees  of 
freedom,  and  in  that  form  it  supplies  the  need  for  an  efficient 
and  reliable  compass. 

The  secret  of  the  whole  thing  is  the  curious  fact  that  a 
gyroscope  with  two  degrees  of  freedom  exhibits  a  keen  desire 
to  place  its  axis  parallel  with  the  axis  of  the  earth.  Owing 


94  THE  GYRO-COMPASS 

to  the  shape  of  the  earth,  a  device  such  as  has  been  described, 
with  its  fork  standing  up  vertically,  cannot  possibly  have 
its  axis  really  parallel  with  that  of  the  earth,  except  on 
the  Equator.  Still  it  gets  as  nearly  parallel  as  possible. 
To  be  scientifically  accurate,  we  ought  to  say  that  it 
places  it  own  axis  "  in  the  same  plane  "  as  that  of  the 
earth. 

To  understand  this  we  need  to  realise  that  all  movement 
is  relative.  In  ordinary  language,  when  we  say  a  thing  is 
still  we  mean  that  it  is  still  in  relation  to  the  surface  of 
the  earth,  but  since  the  earth  is  moving  the  stillest  thing, 
apparently,  is  really  travelling  at  enormous  speed. 

Saint  Paul's  Cathedral  in  London,  or  a  tall  sky-scraper  in 
New  York,  would  usually  be  regarded  as  supreme  instances 
of  immobility.  It  would  be  hard  to  find  better  examples 
of  stationariness,  as  we  ordinarily  look  at  things.  Each 
stands,  firm  and  strong,  upon  a  horizontal  base.  Yet 
each  is  really  turning  a  somersault  every  twenty-four  hours. 
The  plateau  upon  which  St  Paul's  stands,  though  it  seems 
still  and  motionless  beneath  our  feet,  is  continually  tilting  ; 
its  eastern  edge  is  continually  going  downwards  and  its 
western  edge  upwards,  as  the  earth  performs  its  daily  spin. 
It  is  only  a  north  and  south  line  which  does  not  share  in 
some  degree  this  continual  tilting  action.  Every  plane, 
large  or  small,  so  long  as  it  remains  horizontal,  is  being 
tilted  thus,  down  at  the  eastern  edge  and  up  at  the  western. 
And  the  plane  in  which  the  axle  of  a  gyroscope  with  "  two 
degrees  "  is  free  to  move  is  a  horizontal  plane.  Owing  to 
its  being  held  between  the  prongs  of  the  fork,  while  it  can 
swing  round  to  point  north,  south,  east  or  west,  or  towards 
any  point  between  them,  it  cannot  deviate  from  the  hori- 
zontal plane.  Therefore  such  axle  is  always  being  tilted 
by  the  motion  of  the  earth,  except  when  it  happens  to  be  lying 
exactly  north  and  south. 

Now  for  a  reason  which  is  too  complex  to  go  into  here 
a  gyroscope  strongly  objects  to  having  its  axle  tilted  in  this 
manner.  If  it  be  compelled  by  superior  force  to  submit  to 


THE  GYRO-COMPASS  95 

tilting,  it  tries  to  wrench  itself  round  sideways.  Anyone 
who  has  a  gyroscope  top  and  cares  to  try  the  experiment 
will  feel  this  action  quite  easily.  Hold  the  spinning-top 
in  your  hand  and  turn  it  over  so  as  to  tilt  the  axle,  when  it 
will,  if  you  are  not  careful,  twist  itself  out  of  your  grasp. 

So  a  gyroscope  of  the  kind  we  are  considering,  when  the 
motion  of  the  earth  tilts  its  axis,  turns  itself  round  in  its 
socket  until  at  last  it  reaches  the  north  and  south  position, 
when  the  tilting,  and  therefore  the  twisting,  ceases.  Hence 
the  axle  of  the  gyroscope  if  left  to  itself  (the  rotation  of  the 
wheel  being  maintained  the  while)  will  place  itself  in  a  north 
and  south  direction.  And,  moreover,  it  will  keep  in  that 
direction.  It  will  take  some  force  to  slew  it  round  into  any 
other.  And  if  moved  into  any  other  by  some  extraneous 
means  it  will  restore  itself  to  the  old  position  again. 

Hence  a  wheel  thus  arranged  has  all  the  attributes  which 
we  need  for  a  mariner's  compass.  But  unfortunately  there 
are  mechanical  difficulties  in  the  way  of  using  such  a  simple 
contrivance  for  that  purpose. 

Chief  of  all  these  is  the  fact  that  it  is  not  what  engineers 
call  "  dead-beat."  That  means  that  it  will  not  go  to  the 
proper  position  and  then  remain  there  quite  still.  Instead,  it 
will  first  slightly  overshoot  the  mark,  which  being  followed 
by  the  reverse  action,  it  will  come  back  and  overshoot  it 
just  as  far  in  the  opposite  direction.  Instead,  therefore, 
of  a  steady  pointing,  always  in  the  same  direction  precisely, 
it  will  oscillate  more  or  less,  the  exact  north  and  south  line 
being  the  mean  or  average  position,  the  centre  of  the 
oscillations. 

It  would  of  course  be  possible  to  damp  this,  to  apply  a 
break  as  it  were,  if  the  apparatus  were  to  remain  stationary. 
For  example,  if  the  whole  concern  were  immersed  in  water 
the  resistance  of  the  liquid  would  restrain  any  quick  move- 
ment of  the  axle,  yet  it  would  not  prevent  it  from  slowly 
finding  its  true  position.  Thus  the  oscillations  would  be 
reduced  to  such  a  small  range  as  to  be  for  practical  purposes 
negligible.  But  the  drawback  to  a  device  of  that  kind, 


96  THE  GYRO-COMPASS 

applied  to  a  gyroscoDe  on  board  ship,  would  be  that  the  axle 
would  be  carried  round  to  some  extent  every  time  the  ship 
turned.  As  she  changed  direction  it  would  more  or  less 
carry  round  the  water  with  it ;  that  in  turn  would  carry 
the  gyroscope,  and  so  the  direction  of  the  latter  would  be  for 
a  time  untrue.  It  would  in  course  of  time  regain  its  accuracy, 
but  in  the  meantime  it  would  be  leading  the  ship  astray. 

Consequently  the  application  of  this,  in  itself  wonderfully 
simple,  idea,  to  this  extremely  important  purpose  was 
accompanied  with  a  difficulty  which  was  for  a  long  time 
insuperable. 

But  all  was  overcome  at  last  by  the  genius  of  Dr  Anschutz, 
of  Hamburg,  whose  firm  were  the  first  to  turn  out  the 
practicable  article.  Taking  advantage  of  another  move- 
ment of  the  gyroscope  when  arranged  as  has  been  described, 
and  using  the  revolving  wheel  itself  as  a  centrifugal  fan, 
he  was  able  to  make  the  wheel  blow  air  "  against  itself," 
as  it  were,  when  in  any  position  other  than  north  and  south. 
Thus,  if  it  deviates  towards  the  east,  this  jet  of  air  tends 
to  blow  it  back ;  if  it  turns  westwards  the  jet  again  comes 
into  operation,  tending  to  bring  the  erring  gyro  back  to  its 
proper  place  ;  and  so  the  tendency  to  oscillate  is  checked. 

The  finished  instrument  as  it  is  installed  on  the  latest 
warships  is,  of  course,  quite  different  in  detail  from  the 
simple  contrivance  which  we  have  been  considering  so  far, 
although  it  is  the  same  precisely  in  principle.  The  essential 
part  is  a  heavy  metal  wheel  combined  with  which  is  an 
electric  motor  which  keeps  it  rotating  at  a  speed  of  20,000 
or  so  times  per  minute. 

The  bearings  of  the  wheel  are  supported  upon  a  metal  ring 
which  floats  upon  the  surface  of  a  trough  of  mercury.  Thus 
friction  is  brought  down  almost  to  the  irreducible  minimum. 
The  only  place  where  the  wheel  and  its  supports  touch  any- 
thing solid  is  at  one  delicately  made  pivot  which  serves  to 
keep  the  floating  mechanism  in  the  centre  of  the  mercury 
basin,  and  to  prevent  it  from  rubbing  against  the  side  of  it. 
The  current  which  drives  the  motor  reaches  it  through  this 


THE  GYRO-COMPASS  97 

pivot  and  leaves  through  the  mercury.  Thus  arranged, 
although  the  floating  part  is  of  considerable  weight,  a  very 
slight  force  indeed  is  enough  to  move  it ;  while,  looking  at 
it  the  other  way,  we  can  see  that  the  ship  might  turn  rapidly 
to  right  or  to  left,  carrying  round  the  mercury  bowl  with  it, 
without  turning  the  floating  part  at  all.  Thus  the  gyroscopic 
action  is  very  free  indeed  to  exercise  its  function  of  keeping 
the  contrivance  pointing  always  in  the  one  way. 

The  float  has  mounted  upon  it  a  compass  card  much  like 
that  of  the  ordinary  magnetic  instrument,  and  the  sailor 
reads  it  in  precisely  the  same  way.  To  outward  appearance 
there  is  little  essential  difference  ;  in  one  case  there  is  a 
magnet  under  the  card  to  keep  it  still,  in  the  other  there  is 
the  float  with  the  revolving  wheel  mounted  upon  it. 

It  is  customary  to  have  one  "master  compass"  of  this 
kind  on  a  ship,  with  an  electrical  repeater  in  each  of  the 
steering  positions.  As  the  "  master  "  turns  in  its  casing 
it  sends  a  rapid  series  of  currents  to  all  the  others,  causing 
them  to  turn  in  unison  with  it.  The  "  master  "  is  fitted  in 
some  safe  part  of  the  ship  where  it  is  least  likely  to  be  the 
victim  of  any  accidental  damage. 


CHAPTER  VIII 

TORPEDOES    AND   SUBMARINE   MINES 

IT  is  sad  to  think  how  much  scientific  skill  and  learning 
has,  during  the  Great  War,  been  devoted  to  killing 
people.  It  used  to  be  thought  that  one  day  a  great 
scientific  invention  would  arise,  of  such  deadly  power  that 
for  ever  afterwards  war  would  be  unthinkable  ;  its  horrors 
would  be  such  that  all  nations  would  shrink  from  it.  That 
prophecy,  however,  has  not  been  fulfilled,  nor  are  there  any 
signs  of  it.  On  the  contrary,  each  scientific  achievement 
in  the  realm  of  warfare  is  quickly  countered  by  another : 
so  much  so  that  with  all  our  science  in  the  manufacture  of 
weapons,  and  our  skill  in  using  them,  warfare  in  the  twentieth 
century  is  if  anything  less  deadly  in  proportion  to  the 
numbers  engaged  than  it  used  to  be. 

There  are,  however,  two  weapons  which  in  this  war  have 
reached  a  deadly  efficiency  which  they  did  not  seem  to 
possess  before,  and  to  which  satisfactory  antidotes  have  not 
yet  appeared. 

These  two  are  the  submarine  mine  and  the  torpedo.  The 
latter,  particularly,  had  been  a  dismal  failure  previously,  but 
as  the  weapon  of  the  submarine  it  has  now  established  itself. 
It  is,  however,  only  in  connection  with  the  submarine  that 
it  has  achieved  any  measure  of  success,  and,  as  there  are 
strong  indications  that  very  soon  the  submarine  itself  will 
be  robbed  of  its  terrors,  it  is  quite  likely  that  the  reign  of 
the  torpedo  will  be  brief. 

Although  it  has  only  just  made  itself  felt  seriously  in 
warfare,  the  torpedo  is  a  fairly  old  idea.  In  fact  we  can 
trace  the  general  idea  of  it  back  to  very  ancient  times.  The 
modern  weapon,  however,  dates  from  the  year  1864,  when  an 

98 


TORPEDOES  AND  SUBMARINE  MINES         99 

Austrian  inventor  approached  an  English  engineer  named 
Whitehead  with  a  request  to  take  up  his  idea.  Mr  White- 
head  had  at  that  time  a  works  at  Fiume,  on  the  Adriatic,  and 
it  was  really  his  genius  that  developed  the  crude  idea  into  a 
practicable  invention. 

Thus  there  came  into  existence  the  Whitehead  Torpedo, 
now  used  in  a  great  many  navies,  and  also  the  Schwartzkopff , 
which  may  be  regarded  as  the  German  variety  of  the  same 
thing. 

Speaking  generally,  it  may  be  described  as  a  small  auto- 
matic submarine  boat.  Externally,  it  naturally  follows 
somewhat  the  lines  of  a  fish.  Deriving  its  name  from  that 
curious  fish  which  is  able  to  give  electric  shocks  from  its 
snout,  it  likewise  carries  on  its  nose  that  appliance  whereby 
it  gives  a  shock,  not  electric  it  is  true,  but  equally  deadly, 
to  anything  which  it  may  touch. 

Since  no  man-made  mechanism  can  approach  the  marvel- 
lous action  of  the  fish's  fins  and  tail,  the  propulsion  is  achieved 
by  a  propeller  like  that  of  a  steamboat,  but  of  course  on  a 
very  small  scale.  A  single  propeller,  however,  would  tend 
to  turn  the  torpedo  over  and  over  in  the  water,  and  so  it 
has  two,  one  behind  the  other,  driven  in  opposite  ways,  so 
that  the  turning  tendency  of  one  is  neutralised  by  that  of 
the  other.  The  blades  of  the  propellers  are,  however,  set 
in  opposite  ways,  so  that  although  rotating  in  different 
directions  they  both  push  the  torpedo  along. 

Behind  the  propellers,  again,  there  are  rudders  for  steering. 
One  steers  to  right  or  left,  as  does  that  of  an  ordinary  ship, 
while  two  others  are  so  placed  that  they  can  steer  upwards 
and  downwards. 

So  there  we  have  the  general  picture  of  the  outside  :  a 
smooth,  fish-like  body  with  a  "  sting  "  in  its  nose,  propellers 
at  the  rear  to  drive  it  along,  and  rudders  to  guide  it. 

Inside  are  various  chambers.  One  contains  the  explosive 
which  blows  up  when  the  nose  strikes  something.  This 
"  head,"  as  it  is  termed,  is  detachable,  so  that  it  can  be  left 
off  until  it  is  really  required  for  war.  The  peace-head, 


100       TORPEDOES  AND  SUBMARINE  MINES 

which  is  of  the  same  size,  shape  and  weight  as  the  war-head, 
is  what  the  torpedo  carries  during  its  earlier  career.  With 
this  it  can  be  tried  and  tested  in  safety,  the  wrar-head  being 
substituted  when  the  real  business  of  the  torpedo  begins. 

Another  chamber  contains  the  compressed  air  which 
furnishes  the  motive  power.  This  also  serves  to  give 
buoyancy. 

Aiiother  chamber,  again,  contains  the  engines,  beautiful 
little  things  of  the  finest  workmanship  almost  exactly  like 
the  finest  steam-engine,  but  of  course  very  small  in 
comparison. 

In  the  early  stages  the  range  of  the  torpedo  was  limited 
by  the  amount  of  compressed  air  which  it  could  carry.  At 
first  sight  there  seems  no  reason  why  any  limit  should  be 
placed  upon  this,  but  in  practice  there  are  often  limitations 
in  engineering  matters  which  are  not  apparent  on  the  surface. 
For  example,  to  increase  the  air  chamber  would  mean 
enlarging  the  whole  torpedo,  calling  for  more  propulsive 
power  and  larger  engines,  and  these  larger  engines  would 
call  for  more  air,  thus  defeating  the  object  in  view.  Forcing 
more  air  in  by  using  a  higher  pressure,  in  a  similar  way  would 
necessitate  a  thicker  chamber,  to  resist  the  higher  pressure. 
This  would  add  weight,  calling  for  more  buoyancy.  Thus 
there  seemed  to  be  a  practical  limit  beyond  which  it  was 
impossible  to  go. 

The  difficulty  was  overcome,  however,  in  a  very  cunning 
way.  When  the  engines  have  used  some  of  the  air,  and  the 
store  is  somewhat  exhausted,  chemicals  come  into  action 
which  generate  heat,  which  is  imparted  to  the  air  which  is 
left.  This  heat  expands  the  air,  producing  in  effect  a  larger 
supply  of  it,  and  enabling  the  torpedo  to  make  a  longer 
journey. 

Steering  in  a  horizontal  direction — that  is  to  say,  to  left 
or  right — is  done  by  a  gyroscope.  The  action  of  a  rotating 
wheel  is  discussed  in  the  last  chapter,  and  it  is  not  necessary 
here  to  say  more  than  this  :  a  rotating  wheel  always  tries  to 
keep  its  axle  pointed  in  the  same  direction.  Just  at  the 


TORPEDOES  AND  SUBMARINE  MINES        101 

moment  of  starting  such  a  wheel  is  set  going  inside  the 
torpedo,  and  its  arrangement  is  such  that,  should  the 
torpedo  swerve  to  the  left,  the  gyroscope  operates  the  rudder 
and  steers  it  back.  In  the  same  way,  if  it  tends  to  turn  to 
the  right,  the  ever-watchful  gyroscope  brings  it  to  its  true 
course  once  more.  The  effect  of  the  gyroscope,  therefore, 
acting  upon  the  rudder,  is  to  keep  the  torpedo  faithfully  to 
the  direction  upon  which  it  is  started. 

The  up  and  down  rudders  are  likewise  controlled  quite 
automatically,  but  in  a  different  way.  Their  function, 
clearly,  is  to  keep  the  thing  at  a  certain  uniform  level. 
Without  such  control  a  torpedo  would  be  equally  likely 
to  jump  out  of  the  water  altogether,  or  to  go  downwards 
vertically  and  bury  its  nose  in  the  mud.  The  depth  at 
which  it  is  to  move  is  determined  beforehand,  certain 
necessary  adjustments  are  made,  and  the  torpedo  then 
pursues  its  even  way,  neither  coming  to  the  surface  nor 
driving  beneath  its  target. 

For  this  purpose  there  is  first  of  all  a  "  hydrostatic  valve." 
This  little  appliance,  which  is  open  to  the  action  of  the  water, 
responds  to  changes  in  pressure.  The  pressure  at  any  point 
under  water  is  exactly  proportional  to  the  depth.  At  ten 
feet,  for  example,  it  is  precisely  ten  times  what  it  is  at  one 
foot.  So  the  hydrostatic  valve  is  adjusted  to  set  the  rudders 
straight  when  the  water-pressure  upon  it  is  a  certain  amount. 
If,  then,  it  dives  downwards  the  pressure  increases  and  the 
valve  operates  the  rudders  so  as  to  bring  it  upwards,  while 
if  it  rise  too  high  the  decrease  of  pressure  causes  it  to  be 
guided  downwards. 

This  action,  however,  is  too  sudden  and  violent,  so  that 
with  it  alone  the  torpedo  would  proceed  by  leaps  and  bounds. 
After  being  low  it  would  come  up  too  suddenly,  overshoot 
the  mark,  only  to  be  steered  downwards  again  equally 
suddenly. 

The  valve,  therefore,  is  combined  with  a  pendulum, 
whose  action  tends  to  restrain  these  too  sudden  changes, 
with  the  result  that  under  the  influence  of  the  two  things 


102        TORPEDOES  AND  SUBMARINE  MINES 

combined  the  torpedo  keeps  fairly  well  to  an  even  course, 
only  varying  upwards  or  downwards  to  an  extent  which  is 
negligible. 

Finally,  there  is  an  interesting  little  feature  about  the 
firing  mechanism  which  merits  a  description.  The  actual 
firing  is  caused  by  the  driving  in  of  a  little  pin  which  projects 
at  the  nose  of  the  torpedo.  Suppose  that,  in  the  process 
of  pointing  the  torpedo  and  launching  it  upon  its  course, 
that  pin  were  to  be  knocked  accidentally,  an  awful  disaster 
would  result.  It  must  be  provided  against,  therefore,  and  the 
method  adopted  is  beautiful  in  its  certainty  and  simplicity. 

Normally,  the  firing-pin  is  fixed  by  a  screw  so  securely 
that  no  accidental  firing  is  possible.  There  is,  however,  a 
little  propeller-like  object  associated  with  it,  which  is  driven 
round  by  the  water  as  the  torpedo  is  pushed  through  it, 
and  this  unscrews,  and  thereby  releases  the  pin.  The  little 
"  fan  "  has  to  rotate  a  certain  number  of  times  before  the 
pin  is  released,  and  it  is  quite  impossible  for  this  number 
to  be  accomplished  before  the  torpedo  has  proceeded  to  a 
safe  distance  from  the  ship  which  fires  it.  On  board  the 
ship,  therefore,  and  so  long  as  it  is  near  the  ship,  it  is  quite 
safe,  but  by  the  time  it  reaches  its  target  it  is  ready  to 
explode. 

As  far  as  is  known,  the  foregoing  description  gives  a  true 
general  description  of  the  torpedoes  now  in  use.  Those 
of  different  powers  may  vary  in  detail,  but,  broadly,  they  are 
as  just  described. 

There  are  others,  however.  The  Brennan,  for  instance, 
was  once  adopted  and  largely  used  by  the  British  for  harbour 
defence.  This  was  controlled  from  the  shore  by  wires.  It 
was  driven,  so  to  speak,  with  wire  reins,  and  thus  guided  it 
could  fairly  hunt  down  its  prey,  turning  to  right  and  to  left 
as  required. 

Of  greater  scientific  interest,  perhaps,  still,  is  the  "  Armorl" 
wireless  controlled  torpedo.  This  is  the  invention  of  two 
gentlemen,  Messrs  Armstrong  and  Orling,  whose  first  syllables 
combine  to  form  the  title  of  the  torpedo. 


TORPEDOES  AND  SUBMARINE  MINES        103 

Of  this,  two  very  interesting  features  may  be  mentioned. 
Firstly,  the  wireless  control.  In  the  chapter  on  Wireless 
Telegraphy  there  is  described  the  coherer,  a  simple  little 
apparatus  which  we  might  describe  as  a  door  which  is 
opened  by  the  "  waves  "  which  travel  through  the  ether 
from  the  sending  apparatus.  Whenever  the  key  of  the 
sending  apparatus  is  depressed  these  waves  travel  forth, 
and  when  they  fall  upon  the  coherer  it  "  opens."  Normally, 
the  coherer  is  shut,  but  when  acted  upon  by  the  incoming 
waves  it  opens  and  lets  through  current  from  a  battery, 
which  current  can  be  caused  to  perform  any  duty  which 
we  may  wish.  Thus,  ignoring  the  intermediate  steps,  we 
get  this  :  whenever  the  sending  key  is  depressed  current 
flows  through  the  coherer  and  performs  whatever  duty  is 
set  before  it. 

And  now  picture  to  yourself  a  tooth  wheel  with  four  teeth. 
A  catch  normally  holds  one  of  the  teeth,  but  when  the  catch 
is  lifted  for  a  moment  it  lets  that  tooth  slip  and  the  next 
one  is  caught.  At  every  lifting  of  the  catch  the  wheel  turns 
a  quarter  of  a  turn.  Then  imagine  that  that  catch  is 
operated  by  an  electro-magnet  energised  by  the  currentwhich 
passes  through  the  coherer.  We  see,  then,  that  every  time 
the  sending  key  is  depressed  the  wheel  turns  a  quarter  turn. 

Attached  to  the  wheel  is  a  little  crank  which  turns  with  it, 
and  the  pin  of  this  crank  fits  in  a  slot  in  the  end  of  a  bar  like 
the  tiller  of  a  boat.  Suppose  that,  to  commence  with,  the 
tiller  is  straight,  so  as  to  steer  the  boat  straight.  Depress  the 
key,  the  wheel  turns  a  quarter  turn  and  the  tiller  is  set  so  as 
to  steer  to  one  side,  say  the  left.  Another  pressure  upon  the 
key  and  a  second  quarter  turn  brings  the  tiller  straight  again. 
Yet  another  pressure,  another  quarter  turn,  and  the  tiller  is 
steering  to  the  right.  Thus  by  simply  pressing  the  key  the 
correct  number  of  times  the  torpedo  can  be  made  to  travel 
in  any  desired  direction. 

The  second  ingenious  feature  of  this  weapon  is  the  means 
by  which  it  is  made  visible  to  the  man  who  is  controlling  it 
from  the  shore  or  ship.  Probably  the  reason  why  these 


104       TORPEDOES  AND  SUBMARINE  MINES 

torpedoes  are  not  used  more  is  that  the  man  who  guides 
them  is  of  necessity  himself  visible.  He  has  to  be  posted 
somewhere  where  he  can  follow  its  course,  or  he  has  no  idea 
how  to  steer  it.  Consequently,  he  would  be  an  object  for 
attack  by  the  enemy.  Such  a  torpedo  would  be  useless  in 
a  submarine,  for  the  submarine  would  need  to  come  to  the 
surface  in  order  that  the  observer  might  get  a  sufficiently 
good  view  to  be  able  to  steer  the  torpedo,  and  we  all  know 
that  when  upon  the  surface  a  submarine  is  a  very  vulnerable 
craft. 

But  that  is  by  the  way.  The  point  is  how  to  make  the 
torpedo  very  clearly  visible  while  it  is  still  under  water. 
A  short  mast  might  be  used,  but  that  would  be  liable  to  be 
shot  away.  The  inventor  had  a  happy  inspiration  when  he 
made  it  blow  up  a  jet  of  water,  like  a  whale  does.  This  jet 
is  quite  easy  to  see,  yet  no  shot  can  destroy  it.  Compressed 
air  blows  up  this  tell-tale  jet  which  the  observer  can  see,  and 
by  its  means  he  can  guide  the  torpedo  at  will. 

A  submarine  mine  may  be  regarded  as  a  stationary 
torpedo.  It  consists  of  a  metal  case  filled  with  a  powerful 
charge  of  explosive  which  floats  harmlessly  in  the  water  until 
some  unfortunate  vessel  strikes  against  it,  when  it  blows  up 
with  sufficient  force  to  make  a  hole  in  the  stoutest  ship. 

There  are  two  classes  of  mine :  one  which  is  laid  in  peace 
time,  to  protect  harbours  and  channels ;  and  the  other,  which 
is  laid  during  actual  warfare. 

The  former  are  anchored  in  a  more  or  less  permanent  way. 
The  services  of  divers  are  used  to  place  them  in  position.  In 
some  cases  they  float  well  down  in  the  water,  out  of  the  way 
of  passing  ships,  but  come  up  nearer  the  surface  when 
needed.  This  result  is  achieved  by  having  an  anchor  chain 
of  such  a  length  that  when  fully  extended  the  mine  floats 
a  little  way  under  the  surface,  just  high  enough  to  be  struck 
by  a  passing  ship,  together  with  what  is  called  an  "  explosive 
link."  The  link  is  used  to  loop  together  two  parts  of  the 
chain,  and  so,  in  effect,  to  reduce  its  length.  Wires  pass  from 
the  link  to  the  shore,  and  when  an  electric  current  is  sent 


TORPEDOES  AND  SUBMARINE  MINES       105 

along  these  wires  the  link  bursts  asunder,  liberates  the  chain, 
and  the  mine  floats  up  to  the  full  length  of  its  chain. 

Another  plan  is  to  let  the  mines  float  high  up  always,  but 
to  fire  them,  not  by  the  touch  of  the  ship  but  by  electricity 
from  the  shore.  In  this  way  a  safe  channel  is  kept  for 
friendly  vessels,  while  an  enemy  can  be  destroyed. 

Necessarily,  those  mines  which  are  hurriedly  laid  in  war 
time  are  very  different  from  these.  To  be  of  much  use, 
a  mine  must  be  concealed  below  the  surface.  If  it  floats 
upon  the  water  it  will  be  visible,  and  can  be  avoided,  or,  at 
all  events,  easily  picked  up.  It  is  practically  impossible  to 
set  a  floating  object  at  a  certain  depth  in  the  water,  except 
by  anchoring  it  to  another,  heavier,  object,  which  will  lie 
at  the  bottom.  Therefore  mines  have  to  be  anchored  in 
some  way. 

But  the  sea  varies  in  depth,  so  that  the  length  of  the 
anchor  chain  must  be  varied,  or  else  some  of  the  mines  will 
be  on  the  surface,  thereby  advertising  the  presence  of  the 
mine-field,  while  others  will  be  below  the  depth  of  even  the 
biggest  ship.  In  warfare,  however,  mines  need  to  be  laid 
quickly.  There  is  no  time  to  sound  for  the  depth  and  then 
to  adjust  the  length  of  cable  accordingly.  Hence  the  mine 
must  be  so  made  as  to  set  itself  correctly  at  a  pre-determined 
depth. 

Possibly  some  readers  may  think  that  such  things  might 
be  made  to  float,  of  themselves,  at  the  right  depth.  It  is 
a  fact,  however,  that  a  thing  either  floats  upon  the  surface 
of  water  or  falls  to  the  bottom.  Water  is  practically  in- 
compressible, so  that  the  water  at  the  bottom  of  the  sea 
is  no  heavier  than  that  near  the  surface.  The  conditions 
which  prevail  in  air  and  allow  a  balloon  to  float  at  any  desired 
height  do  not  apply.  The  only  thing,  in  this  case,  is  to  have 
an  anchor  chain  or  rope  of  the  right  length. 

So  let  us  picture  a  mine-laying  ship  steaming  along, 
probably  in  the  dead  of  night,  surreptitiously  laying  mines 
in  the  hope  that  the  enemy  will  run  into  them  on  the  morrow. 

Along  the  deck  of  the  ship  are  small  railway  lines,  and  on 


106        TORPEDOES  AND  SUBMARINE  MINES 

these  lines  stand  what  appear  to  be  trains  of  small  trucks, 
each  truck  having  small  wheels  to  run  on,  and  each  bearing 
a  large  round  metal  ball.  As  the  ship  travels  along,  the 
crew,  handling  these  deadly  things  quite  freely,  as  if  they 
were  innocent  of  any  danger,  propel  them  along  to  the  stern, 
and  at  regular  intervals  push  one  overboard.  That  is  all. 

The  freedom  with  which  the  men  handle  them  is  not  folly, 
for  they  are  then  quite  harmless.  Nor  need  they  trouble 
about  the  length  of  rope,  for  that  adjusts  itself.  Just 
tumble  the  things  overboard,  and  in  due  time  they  anchor 
themselves  at  the  right  depth  and  set  themselves  in  the  right 
condition  for  blowing  up  any  ship  which  may  get  amongst 
them. 

The  truck-like  object  upon  wheels  is  not  the  mine  itself : 
it  is  the  sinker  which  lies  at  the  bottom  of  the  sea.  The 
round  ball  which  it  bears  is  the  mine,  and  the  two  are  con- 
nected together  by  a  wire  rope.  To  commence  with,  this 
rope  is  coiled  upon  a  drum  in  the  sinker,  which  drum  is 
either  held  tightly  or  is  free  to  revolve  according  to  the 
position  of  a  catch.  That  catch  is  held  open,  so  that  the 
drum  is  free,  by  a  weight  at  the  end  of  a  short  rope.  Let  us 
assume  that  that  rope  is  ten  feet  long. 

Then,  when  the  whole  thing  is  tumbled  into  the  water, 
the  weight  sinks  first  ten  feet  below  the  sinker,  which,  being 
more  bulky  in  proportion  to  its  weight,  follows  downwards 
more  slowly.  While  sinking,  the  weight  is  pulling  upon  its 
rope  and  holding  open  that  catch,  so  that  the  drum  pays  out 
its  rope  and  the  mine  lies  serenely  upon  the  surface.  As 
soon  as  the  weight  touches  bottom,  however,  the  pull  on 
the  short  rope  ceases,  the  catch  grips  the  drum,  no  more 
rope  is  paid  out,  and  the  sinker,  in  settling  down  its  last 
ten  feet,  has  to  drag  the  mine  down  too.  Thus,  quite  auto- 
matically, by  what  is  really  a  beautifully  simple  arrange- 
ment, the  mine  becomes  automatically  anchored  at  a  depth 
below  the  surface  equal  to  the  length  of  the  short  rope. 
By  making  that  rope  the  desired  length,  the  depth  of 
the  mine  under  the  water  can  be  fixed. 


TORPEDOES  AND  SUBMARINE  MINES       107 

There  are  various  methods  of  firing  these  mines,  all  of 
which  work  perforce  by  the  concussion  of  the  ship  itself.  In 
some  cases  the  sudden  tilting  over  causes  an  electric  contact 
to  be  made,  and  permits  a  battery  in  the  mine  to  cause  the 
explosion.  Another  way  is  to  furnish  the  mine  with  pro- 
jecting horns  of  soft  metal,  inside  which  are  glass  vessels 
containing  chemicals.  The  ship,  striking  a  horn,  bends  it, 
breaks  the  glass,  and  liberates  the  chemicals  which  cause 
the  explosion. 

In  the  type  of  mine  largely  used  by  the  British  Navy 
there  is  a  projecting  arm  pivoted  on  the  top  of  the  mine  and 
projecting  from  it  horizontally.  The  mine  itself  rolls  along 
the  side  of  the  passing  ship,  but  the  arm  simply  trails  or 
scrapes  along.  Thus  the  mine  turns  in  relation  to  the  arm, 
and  a  trigger  is  thereby  released,  which  fires  the  mine. 

In  this,  be  it  noted,  the  ship  only  pulls  the  trigger,  so  to 
speak,  and  releases  a  hammer  which  does  the  work,  just  as 
the  trigger  of  a  gun  releases  the  hammer.  The  motive  force 
which  makes  the  hammer  do  its  work  when  the  trigger  is 
"  pulled  "  is  the  pull  on  the  anchor  rope.  That  arrange- 
ment has  a  virtue  which  is  not  apparent  at  first  sight. 

Since  it  is  the  pull  on  the  anchor  rope  which  actually  fires 
the  mine,  it  follows  that  if  such  a  mine  break  away  from  its 
moorings  it  instantly  becomes  harmless. 

Safety  for  the  men  who  lay  the  mines  is  secured  in  several 
ways.  One  is  by  the  use  of  a  hydrostatic  valve.  The  firing 
mechanism  is  locked  until  the  pressure  of  water  releases  it, 
and  that  pressure  does  not  exist  until  the  mine  is  several 
feet  under  water.  Another  way  is  to  seal  up  the  firing 
mechanism  with  a  soluble  seal  made  of  some  substance  such 
as  sal-ammoniac.  The  mine  cannot  then  explode  until  it 
has  been  under  water  long  enough  for  the  seal  to  be  melted. 

It  now  remains  to  relate  how  these  mines  are  swept  up 
and  removed,  yet  there  is  very  little  really  to  tell,  for  the 
process  is  so  exceedingly  simple.  So  far  as  is  generally 
known,  no  method  has  been  found  that  is  superior  to  the 
primitive  plan  of  dragging  a  rope  along  between  two  ships 


108       TORPEDOES  AND  SUBMARINE  MINES 

so  as  to  catch  the  anchor  ropes.  The  vessels  employed  are 
usually  of  very  light  draft,  so  that  they  stand  a  good  chance 
of  passing  over  the  mines  themselves,  and  the  rope  used  is 
as  long  as  possible,  so  that  a  mine,  if  exploded  by  being 
caught  in  the  loop  of  the  rope,  explodes  so  far  away  as  to 
do  no  harm. 

When  dragged  to  the  surface  the  mines  are  exploded  from 
a  distance  by  shots  from  a  small  gun,  or  even  from  a  rifle. 
In  the  case  of  those  mines  which  have  horns,  a  blow  from 
a  bullet  is  enough  to  break  the  glass  and  cause  explosion, 
and  in  all  cases  mines  seem  sooner  or  later  to  succumb  to 
a  sharp  blow.  Thus  they  are  destroyed,  by  their,  own 
action,  at  a  safe  distance  from  the  sweepers.  Accidents 
happen,  however,  and  mine-sweeping  is  no  job  for  anyone 
but  the  bravest. 

It  has  been  somewhat  difficult  to  crowd  a  description  of 
torpedoes  and  mines  into  the  small  space  of  one  chapter, 
and  so  many  details  have  had  to  be  omitted,  but  the  above 
descriptions  give  the  broad,  general  principles  underlying 
practically  all  forms  of  these  terrible  weapons. 


CHAPTER  IX 

GOLD  RECOVERY 

THERE  has  always  been  something  very  fascinating 
about  gold.     Even  in  ancient  times  it  was  prized 
above  all  other  things,  and  apparently  it  was  com- 
paratively  plentiful.     It  is  estimated,   for  example,   that 
King  Solomon  possessed  over  £4,000,000  worth  of  it,  while 
the  little  gift  which  the  Queen  of  Sheba  brought  him  was  of 
the  handsome  value  of  £600,000,  so  that  she  too  must  have 
been  plentifully  supplied  with  it. 

Probably  it  was  more  easily  come  by  in  those  days,  owing 
to  the  richness  of  the  primitive  deposits,  the  best  of  which, 
perchance,  have  been  worked  out.  In  one  respect  gold 
differs  from  all  other  metals  (with  the  single  exception  of 
platinum,  which  is  scarcer  still)  in  that  it  appears  naturally 
as  gold,  not  as  ore.  The  little  pieces  of  gold  lie  in  the  mine 
ready  to  be  picked  out,  and  so  if  the  deposit  in  which  it 
occurs  be  near  the  surface,  and  the  particles  be  of  any  con- 
siderable size,  they  are  sure  to  be  found.  A  savage  may  be, 
and  often  is,  very  anxious  to  secure  weapons  and  tools  of 
iron,  little  knowing  that  the  very  ground  upon  which  he 
stands  is  possibly  of  iron  ore.  He  covets  the  single  article 
of  iron,  and  in  some  cases  is  willing  to  give  much  gold  for  it, 
or  ivory,  or  some  such  treasure,  while  thousands  or  millions 
of  tons  of  iron  lie  at  his  feet,  only  he  does  not  recognise  it, 
nor  would  he  know  how  to  utilise  it  if  he  did. 

For  iron,  like  all  other  metals  except  the  two  just  referred 
to,  is  found  naturally  in  combination  with  something  else, 
generally  oxygen,  and  the  combination  bears  no  resemblance 
at  all  to  the  metal.  The  red  rust  so  familiar  to  us  on  iron 
is  a  combination  of  iron  and  oxygen,  and  it  is  fairly  typical 
109 


110  GOLD  RECOVERY 

of  the  kind  of  state  in  which  iron  is  found  in  the  earth.  Nor 
would  anyone  recognise  copper  ore,  lead  ore,  tin  ore,  or 
any  of  the  ores,  any  better  than  iron  ore.  All  are  difficult 
to  recognise.  It  is  said  that  the  highest  compliment  that 
a  Cornish  miner — the  finest  metalliferous  miners  in  the  world 
come  from  Cornwall,  or  are  the  product  of  Cornish  influence — 
the  highest  compliment  that  such  a  man  can  pay  to  another 
is  to  say  that  "  he  knows  tin,"  meaning  that  he  can  tell  tin 
ore  when  he  sees  it. 

Contrasted  with  these  other  metals,  gold  is  easy  to  find. 
It  does,  it  is  true,  under  certain  conditions,  form  chemical 
compounds  with  other  things,  as,  for  instance,  in  gold  chloride, 
which  is  present  in  sea-water,  but  it  does  not  oxidise  as  the 
others  do,  and  so  when  it  is  in  the  earth  it  is  in  the  bright 
yellow  grains  such  as  (if  they  be  large  enough)  can  easily 
be  recognised  at  sight. 

And  it  is  often  found  in  beds  of  loose  gravel,  alluvial 
deposits,  as  they  are  termed.  In  such  cases  the  gold  is  to 
be  had  simply  for  the  picking  up.  Sometimes  a  lucky  find 
occurs  in  the  form  of  a  big  nugget,  but  more  often  the  metal 
lies  in  tiny  grains  at  long  distances  apart,  so  that  a  ton  of 
gravel  has  to  be  sorted  over  to  find  a  paltry  ounce  or  so  of 
gold.  Yet  so  desired  is  it  that  gold  will  always  fetch  its 
price,  and  an  ounce  to  the  ton  (even  less)  is  sometimes  worth 
getting. 

But  in  the  early  history  of  the  world  there  were  possibly 
particularly  generous  deposits  with  plenty  of  gold  in  good- 
sized  pieces,  and  such  would  be  quickly  discovered  and 
worked  by  primitive  man.  No  doubt  the  chieftains  of  those 
days  took  much,  if  not  all,  of  the  gold  that  their  people  found, 
and  more  powerful  chiefs  and  kings  would,  in  turn,  either  by 
force  or  in  trade,  take  it  from  the  weaker,  so  that  it  is  not 
surprising  to  learn  that  some  of  the  mighty  kings  and 
potentates  of  long  ago  were  well  supplied  with  gold. 

Yet  there  are  few  things  more  useless.  Its  value  in  the 
first  instance  was  probably  entirely  due  to  its  beautiful 
colour,  and  the  fact  that  it  does  not  easily  tarnish.  For 


GOLD  RECOVERY  111 

this  reason,  coupled  with  the  fact  that  it  was  by  no  means 
plentiful,  men  liked  to  deck  themselves  with  it,  not  only 
adding  to  their  "  beauty  "  by  so  doing,  but  advertising  to 
their  fellows  the  fact  that  they  were  men  of  wealth,  men  who 
possessed  what  few  others  had,  or  at  all  events  possessed  it 
more  abundantly.  These  three  basic  facts  about  gold,  its 
beauty,  its  freedom  from  deterioration  and  its  comparative 
scarcity,  give  it  its  peculiar  status  among  the  commodities 
of  commerce,  in  that  for  it,  and  for  it  alone,  there  is  a  con- 
tinuous and  universal  demand.  No  gold-mining  company 
ever  shut  down  its  properties  because  of  the  falling  off  in  the 
demand  for  gold.  No  one  ever  had  to  hawk  gold  about  to 
find  a  purchaser  ;  it  is  always  saleable. 

And  hence  its  value  to  humanity  as  the  great  medium  of 
exchange.  When  a  tailor  wants  bread,  as  has  been  pointed 
out  by  a  great  political  economist,  he  does  not  go  searching 
for  a  baker  who  happens  to  need  a  coat.  If  he  did,  he  might 
starve  before  he  found  one.  Instead,  he  gives  his  coat  to 
anyone  who  needs  one,  no  matter  what  his  trade  may  be, 
taking  gold  in  exchange.  Then  he  goes  with  confidence  to 
the  baker,  knowing  full  well  that  he,  in  turn,  will  be  perfectly 
ready  to  give  bread  in  exchange  for  gold.  That  is  the 
principle  upon  which  gold,  and  in  a  few  cases  silver,  has 
become  the  foundation  of  trade.  We  use  it  for  toning 
photographs  and  a  few  other  things,  but,  practically  speaking, 
it  is  useless  stuff,  yet  certain  special  circumstances  have  given 
it  a  special  function  in  civilised  society,  and  so  governments 
now  make  it  up  into  little  flat  discs,  putting  their  own  special 
stamp  upon  them  as  a  guarantee  of  size  and  quality,  and  it  is 
by  handing  those  little  discs  about  that  we  carry  on  our 
trade.  Or  even  where  we  use  no  actual  disc,  we  pretend 
that  we  do,  and  use  a  piece  of  paper  the  value  of  which  we 
say  is  so  many  discs,  but  that  value  depends  entirely  upon 
the  fact  that  someone  has  guaranteed,  on  demand,  to  give 
so  many  discs  for  it. 

And  the  strange  thing  about  it  is  that  although  this  useful- 
ness of  gold  depends  upon  its  rarity,  we  lose  no  opportunity 


112  GOLD  RECOVERY 

of  looking  for  new  sources  of  supply,  and  so  diminishing  that 
rarity.  As  has  been  said,  gold  is  present  in  sea-water, 
although  no  one  knows  how  to  get  it  out,  except  at  a  cost 
which  makes  it  not  worth  while.  But  suppose  that  some 
genius  found  a  way,  and  gold  thus  became  twice  as  plentiful 
as  it  is  now,  the  world  would  be  no  better  off.  Everything 
would  cost  twice  as  much  as  it  does  now ;  that  is  all.  A 
pound  is  merely  so  much  gold.  If  gold  be  twice  as  plentiful 
people  will  want  twice  as  much  of  it  in  exchange  for  what 
they  have  to  sell.  Yet,  all  the  same,  the  man  who  could 
solve  that  problem  of  getting  gold  from  sea-water,  or  from 
anywhere  else,  in  fact,  would  be  hailed  as  a  benefactor,  and 
for  a  time  at  least  he  would  reap  a  generous  harvest. 

Even  as  it  is,  science  has  done  much  for  the  production  of 
gold.  Not,  as  in  other  metals,  in  finding  ways  for  extracting 
it  from  its  ores,  for,  strictly  speaking,  it  has  none,  but  in 
finding  ways  of  catching  the  tiny  particles  of  metal  from  the 
"  gangue,"  as  it  is  called,  the  rock  or  earth  in  which  they 
are  embedded.  The  trouble  is  that  they  are  so  small,  so 
infinitesimally  small,  almost. 

There  are  two  great  types  of  place  where  gold  is  found. 
In  the  alluvial  deposits,  the  beds  of  old  rivers,  the  gold  is 
quite  loose.  The  convulsions  of  ages  ago  have,  in  many 
cases,  elevated  these  beds,  until  now  they  are  on  the  sides  of 
mountains.  In  such  cases  the  loose,  gravelly  stuff  of  which 
they  are  composed  is  washed  down  by  a  powerful  stream 
of  water  from  a  huge  hose-pipe  terminating  in  a  nozzle  called 
a  "monitor."  This  process,  called  " hydraulicing,"  brings 
down  everything  into  a  pond  formed  at  the  foot  of  the  hill, 
and  in  some  cases  a  boat  or  raft  is  floated  upon  the  pond 
with  machinery  on  board  for  dredging  up  the  material. 
Often  a  powerful  centrifugal  pump  sucks  up  the  water 
through  a  pipe  reaching  to  the  bottom  of  the  pond,  bringing 
gravel  and  gold  with  it.  Arrived  in  this  way  upon  the  raft, 
it  all  goes  on  to  separating  tables,  by  which  the  gold,  being 
heavier,  is  divided  from  the  gravel,  which  is  lighter.  These 
tables  will  be  referred  to  again  later. 


GOLD  RECOVERY  113 

In  non -alluvial  workings  the  gold  is  embedded  in  rock  of 
some  kind,  such  as  that  called  quartz.  This  is  hard,  some- 
what of  the  nature  of  granite,  and  before  the  gold  can  be 
liberated  it  has  to  be  crushed  to  the  likeness  of  fine  sand,  so 
that  the  tiny  grains  of  gold  can  be  captured.  The  quartz 
is  found  in  veins  or  lodes,  fissures,  evidently,  in  the  original 
crust  of  the  earth,  produced  probably  as  the  earth  cooled. 
These  have  been  gradually  filled  up  by  hot  volcanic  streams 
of  water,  which  carried  not  only  the  gold  in  solution  but  also 
the  materials  of  which  the  quartz  is  formed.  It  used  to  be 
thought  that  the  veins  were  the  result  of  hot  liquids  forced 
up  from  below  by  volcanic  action,  the  rock  and  metal  being 
themselves  in  the  liquid  state  through  intense  heat.  It  is 
now  more  generally  held  that  water  was  the  vehicle  by  which 
the  materials  were  brought  in,  and  the  vein  formed.  The 
gold  in  the  alluvial  deposits,  too,  is  now  thought  to  have 
come  there  in  solution  in  water,  and  not  by  the  erosion 
and  washing  down  of  rocks  higher  up  the  original  river. 

However  that  may  be,  and  it  is  the  subject  of  discussion 
among  geologists  and  metallurgists,  there  the  gold  is  to-day, 
firmly  fixed  in  the  hard  rock,  and  the  problem  which  con- 
fronts the  metallurgist  is  to  get  it  out  with  the  least  expense. 
The  old  historic  way  of  breaking  up  the  quartz  rock  is  with 
what  are  called  "  stamps,"  pestles  and  mortars  on  a  huge 
scale.  There  are  a  number  of  vertical  beams  of  wood,  each 
shod  with  iron,  fixed  in  a  wooden  frame,  so  that  they  are  free 
to  slide  up  and  down.  Running  along  behind  these  stamps 
is  a  horizontal  shaft  with  projections  upon  it  called  cams. 
There  is  one  cam  for  each  stamp,  and  as  the  shaft  turns  slowly 
round  this  projection  catches  under  a  projection  on  the 
stamp,  and  after  lifting  it  up  a  short  distance  drops  it 
suddenly.  Thus,  as  the  machine  works,  the  stamps  are 
lifted  and  dropped  in  rapid  succession.  The  rock  is  fed  into 
a  box  into  which  the  feet  of  the  stamps  fall,  and  thus  it 
is  pounded  until  it  is  quite  small.  Meanwhile  a  stream  of 
water  flows  through  the  box  and  carries  away  the  finely 
broken  particles  through  a  kind  of  sieve  which  forms  the 


114  GOLD  RECOVERY 

front  of  the  box,  and  which  allows  the  fine,  small  pieces  to 
escape,  while  holding  back  the  larger  ones  and  keeping  them 
until  they  too  have  been  crushed. 

An  average  stamp  will  weigh  600  to  700  lb.,  and  the 
repeated  blows  of  such  a  hammer  are  enough  to  pulverise 
the  hardest  rock. 

Machines  such  as  these  have  been  employed  since  the 
sixteenth  century,  at  all  events,  and  the  improvements  of 
modern  times  are  only  as  regards  details.  It  may  well  be 
wondered,  then,  why  such  an  old  device  is  still  in  use  and 
how  it  comes  about  that  it  has  not  been  displaced  by  some- 
thing newer  and  better.  The  answer,  which  is  an  instructive 
one,  well  worth  bearing  in  mind  by  many  inexperienced 
inventors,  is  that  it  is  so  simple.  It  can  be  shipped  in  com- 
paratively small  parts,  and  so  taken  cheaply  to  any  outlandish 
place.  A  good  deal  of  it  can  be  made  roughly  of  wood,  so 
that  if  native  timber  is  available  it  can  be  made  partly  at 
the  mine,  and  carriage  costs  saved.  Finally,  it  is  so  easy 
to  work  and  to  understand  that  the  most  inexperienced 
workman  can  handle  it,  and  there  is  so  little  that  can  go 
wrong  that  the  most  careless  attendant  cannot  damage  it. 

In  the  bottom  of  the  boxes  there  is  placed  some  mercury, 
for  which  gold  has  a  curious  affinity.  If  a  particle  of  gold 
once  gets  into  contact  with  the  surface  of  the  mercury  it 
will  not  get  away  again  easily.  Thus  the  mercury  catches 
and  holds  many  of  the  gold  particles  which  are  liberated 
when  the  rock  is  broken  up. 

As  it'  reaches  the  required  fineness,  then,  the  crushed  rock 
escapes  from  the  stamp  machine  and  flows  away  in  the  stream 
of  water,  and  although  much  gold  is  caught  by  the  mercury, 
it  is  by  no  means  all.  The  stream  is  therefore  directed 
over  tables  formed  of  copper  sheets  coated  with  mercury, 
so  that  additional  opportunities  are  given  to  mercury  to 
catch  the  grains  of  gold.  Moreover,  the  table,  which,  by 
the  way,  is  placed  at  a  slight  incline,  is  broken  at  intervals 
by  little  troughs  of  mercury  called  riffles,  which  assist  in  the 
depositing  and  catching  of  the  metal  particles. 


GOLD  RECOVERY  115 

But  even  then  all  the  gold  is  not  captured.  The  crushed 
rock  is  now  like  sand,  and  some  of  the  grains  still  con- 
tain gold,  which  has  not  been  detached  by  the  crushing. 
The  gold,  however,  makes  such  grains  slightly  heavier  than 
the  others,  and  because  of  that  they  can  be  separated.  The 
old  way  is  to  use  a  blanket  table,  a  table,  that  is,  covered 
with  coarse  flannel  or  baize,  the  hairs  of  which  catch  these 
heavier  particles  as  the  water  stream  carries  them  along, 
the  lighter  particles  escaping.  The  grains  so  caught  form 
what  are  known  as  "  concentrates,"  since  in  them  the  gold 
is  concentrated. 

The  concentrates  are  subsequently  treated  as  we  shall 
see  later. 

Now  we  can  see  how  modern  scientific  methods  have 
supplemented  the  old  ways.  Take  first  the  case  of  the 
stamp  mill  or  stamp  battery.  In  spite  of  that  prime  virtue 
of  simplicity  which  has  kept  it  at  work  almost  unchanged 
for  centuries,  it  has  its  weaknesses,  and  no  doubt  for  some 
purposes  crushing  mills  are  better.  Of  these  there  are  a 
great  variety,  several  of  which  depend  for  their  action  upon 
centrifugal  force,  or,  as  it  is  more  correctly  termed,  "  centri- 
fugal tendency."  In  these  crushing  mills  there  is  a  ring, 
generally  of  steel,  inside  which  are  suspended  one  or  more 
heavy  iron  rollers.  The  shafts  which  carry  these  rollers  are 
attached  by  their  upper  ends  to  the  driving  mechanism  on 
the  top  of  the  mill,  and  when  that  is  set  in  motion  the  rolls 
are  carried  round  and  round  inside  the  ring.  Because  of  the 
centrifugal  tendency,  they  swing  outwards,  pressing  heavily 
against  the  inner  surface  of  the  ring.  The  rock  is  fed  in 
in  such  a  way  that  the  rollers,  as  they  roll  round  the  inside 
of  the  ring,  repeatedly  travel  over  it  and  crush  it. 

In  another  type  of  mill,  called  the  ball  mill,  the  principle 
is  different.  There  you  have  a  cylinder  of  steel  which  turns 
upon  a  horizontal  axis.  This  cylinder  is  partly  filled  with 
steel  balls  of  various  sizes,  and  as  the  mill  turns,  the  rock, 
being  mixed  with  these  balls,  is  pounded  and  broken  up.  As 
the  mill  turns  over  and  over  the  balls  fall  upon  the  pieces  of 


116  GOLD  RECOVERY 

rock,  thus  producing  a  fine  powder.  Other  mills,  again, 
are  but  refined  editions  of  the  common  mortar  mill  so  often 
seen  where  building  operations  are  going  on,  in  which  heavy 
iron  rollers  travel  over  the  material  to  be  crushed  as  it 
lies  in  a  round  pan. 

The  blanket  table,  too,  gives  place  at  the  modern  mine  to 
the  "  vanner,"  of  which  there  are  several  varieties.  Essenti- 
ally they  are  much  the  same,  and  a  description  of  two  will 
serve  to  give  an  idea  of  them  all.  Let  us  take  the  "  Record  " 
vanner. 

Imagine  a  large  table  formed  of  wood,  the  upper  surface 
covered  with  linoleum.  It  is  fixed  on  slides  so  that  it  can 
move  to  and  fro  endwise.  It  is  given  a  slight  slope  in  the 
direction  at  right  angles  to  its  length — that  is  to  say,  one  edge 
is  a  little  lower  than  the  other.  The  material  is  fed  on  at 
one  end,  at  the  higher  edge,  and  naturally  tends  to  run  down 
and  off  at  the  lower  edge.  It  is  restrained  somewhat  from 
doing  this  by  the  presence  of  rows  of  riffles  or  ridges  running 
lengthwise.  Nevertheless  it  does  in  a  short  time  find  its 
way  off  the  table  at  the  lower  end.  But  all  the  time  that  it  is 
at  work  the  table  is  being  slidden  backwards  and  forwards 
on  the  slides.  By  a  simple  but  curious  mechanism  it  is 
arranged  so  that  it  moves  quickly  in  one  direction  and  slowly 
in  the  other,  with  the  result  that  the  heavier  particles  of 
sand — those  which  contain  gold — are  carried  to  the  farther 
end  of  the  table.  Thus,  as  has  been  said,  all  the  stuff  is  fed 
on  to  the  higher  edge  and  carried  down  by  the  water,  until 
it  falls  off  at  the  lower  edge,  but  during  the  journey  from 
edge  to  edge  the  peculiar  motion  of  the  table  causes  the 
different  kinds  of  sand  to  separate  themselves,  so  that 
the  concentrates  fall  off  near  one  end,  and  the  rest  near  the 
other  end. 

Another  interesting  example  of  ingenuity  is  the  well- 
known  "  Frue  "  vanner.  In  this  the  table  is  a  broad,  endless 
band  of  india-rubber,  extended  upon  two  rollers,  one  of  which 
is  slightly  higher  than  the  other.  The  stream  of  water  and 
crushed  ore  flows  on  at  the  upper  end,  and  runs  down  to 


GOLD  RECOVERY  117 

the  lower,  the  lighter  particles  being  carried  down  and 
dropped  off  at  the  lower  end,  while  the  heavier  rest  upon  the 
band.  Meanwhile  the  turning  of  the  rollers  carries  the 
band  slowly  along,  so  that  the  heavier  particles  gradually 
ascend  and  are  carried  over  at  the  upper  end.  To  assist 
in  the  separation,  the  whole  concern  is  given  a  side-to-side 
shaking  motion  while  it  is  at  work. 

We  have  seen  so  far  how  the  ore  is  crushed,  and  the 
coarser  grains  of  gold  got  out  of  it  by  the  aid  of  mercury. 
The  mixture  of  mercury  and  gold  is  termed  amalgam,  and 
the  process  of  extracting  gold  by  mercury  is  called  amalgama- 
tion. The  gold  is  actually  dissolved  in  the  mercury,  and  so 
when  the  amalgam  has  been  (as  it  is  periodically)  collected 
from  the  plant,  it  has  to  be  filtered  and  then  evaporated  in  a 
retort.  The  mercury  vapour  is  caught  and  condensed  back 
into  a  liquid,  while  the  gold  is  left  in  the  retort.  In  fact  the 
amalgam  is  distilled  in  order  to  separate  the  gold  and  mercury. 

But  when  all  that  is  done  we  still  have  the  concentrates 
from  the  vanners,  or  whatever  be  used,  to  deal  with.  Mercury 
is  useless  with  them,  for  the  gold  is  covered  probably  with 
a  coating  of  the  other  substances,  whatever  they  may  be, 
with  which  it  has  been  associated,  or  else  there  is  mixed 
with  the  gold  some  substances  which  make  amalgamation 
impossible,  or  at  least  difficult. 

Often  roasting  is  necessary  before  anything  more  can  be 
done.  If  arsenic  or  sulphur  be  present,  for  example,  they 
interfere  with  the  recovery  of  the  gold,  and  roasting  will 
disperse  them.  So  the  concentrates  are  passed  through 
great  furnaces,  in  which  they  are  heated  in  contact  with  air 
until  these  objectionable  matters  have  been  oxidised  or 
burnt. 

Then  finally  we  come  to  some  process  by  which  the 
remaining  gold  is  dissolved  out  from  its  admixtures  in  some 
solvent  liquid  from  which  it  can  be  subsequently  precipi- 
tated. This  is  rather  interesting,  because  it  means  that 
man  has  adopted,  to  recover  this  gold  from  the  ore,  the  very 
method  which  it  is  believed  nature  employed  to  put  it  there. 


118  GOLD  RECOVERY 

As  already  said,  the  latest  idea  is  that  the  gold  was  carried 
into  and  deposited  in  the  lodes  where  it  is  now  to  be  found 
by  water — that  the  gold  was  actually  dissolved  in  water  at 
the  time.  But,  of  course,  gold  in  its  metallic  state  will  not 
dissolve  in  water.  Salts  of  gold,  however  (the  meaning  of 
the  term  salt,  as  applied  to  a  metal,  has  been  explained 
earlier),  will  dissolve  in  water,  as  every  photographer  who 
makes  up  his  own  toning  solution  knows  from  experience. 
Gold  will  not  dissolve  in  water,  but  chloride  of  gold  will. 
And  so  the  gold  must  have  been  carried  to  its  resting-place 
as  a  salt,  and  converted  into  the  metallic  form  after  arrival. 
In  the  same  way,  to  recover  these  finest  particles  of  all,  it 
has  to  be  converted  back  into  a  salt ;  then  that  salt  must 
be  dissolved  and  drained  away  from  the  other  stuff;  and, 
finally,  the  gold  must  be  thrown  out  of  solution  again  in  some 
way.  The  great  example  of  this  operation  is  the  familiar 
"  cyanide  "  process. 

The  word  familiar  is  appropriate  to  this  matter  in  only 
one  way,  however.  Holders  of  shares  in  mining  companies, 
for  example,  may  hear  about  it  repeatedly  at  shareholders' 
meetings  and  in  prospectuses,  but  very  few  have  any  clear 
idea  as  to  what  it  is.  So  I  cannot  be  accused  of  telling  an 
oft -told  tale  if  I  devote  a  short  space  to  its  consideration. 

The  combination  of  one  atom  of  carbon  and  one  atom  of 
nitrogen  is  called  cyanogen. 

If  cyanogen  be  given  the  chance  it  will  take  unto  itself 
an  atom  of  hydrogen,  producing  the  deadly  hydrocyanic 
or  prussic  acid.  Alternatively,  if  potassium  be  brought 
into  combination  with  it,  there  results  potassium  cyanide, 
which,  with  the  assistance  of  water  and  oxygen,  can  dissolve 
gold. 

In  applying  this  scientific  fact  to  the  purpose  of  recovering 
gold  from  the  concentrates,  the  latter  are  placed  in  vats 
with  a  weak  solution  of  the  cyanide  in  water.  The  time 
during  which  they  are  allowed  to  remain  depends  upon  the 
size  of  the  gold  particles.  If  they  be  comparatively  large, 
it  stands  to  reason  that  it  must  be  longer  than  if  they  be 


GOLD  RECOVERY  119 

small,  for  they  will  take  longer  to  dissolve.  After  the  proper 
time,  which  is  found  by  experiment,  the  liquid  is  drawn  off, 
and  in  some  cases  the  concentrates  are  given  a  second  dose 
to  ensure  that  the  gold  shall  be  thoroughly  removed  and  none 
left  undissolved.  If  the  material  being  operated  upon  be 
very  fine,  as  it  often  is,  forming  what  the  mining  people  call 
"  slimes,"  then  mechanical  stirrers  have  to  be  used  in  the 
vats  to  keep  the  stuff  moving,  as  otherwise  the  cyanide  would 
not  get  to  all  the  particles  and  some  would  not  be  acted  upon. 

The  liquid,  having  been  the  appropriate  time  in  the  vat, 
is  drawn  off,  placed  in  wooden  tanks  or  boxes,  and  fine  shreds 
of  zinc  are  added  to  it.  Discs  of  sheet  zinc  are  put  into  a 
lathe  and  a  fine  shaving  taken  off  them,  and  it  is  these  fine 
shavings  which  are  used.  Now  zinc,  as  we  know  from  the 
fact  that  it  is  the  essential  part  in  electric  batteries,  has  very 
pronounced  electrical  properties,  and  it  is  believed  that 
these  come  into  play  here.  At  all  events  the  gold  becomes 
deposited  upon  the  zinc,  while  the  zinc  itself  is  to  a  certain 
extent  eaten  away  by  the  solution.  The  result  is  (a)  a 
solution  weaker  than  it  was  before,  (b)  the  remains  of  the 
shavings,  and  (c),  at  the  bottom  of  the  box  in  which  this 
process  takes  place,  a  dark  mud.  That  black  mud,  on  being 
heated,  produces  the  bright  metallic  gold,  and  the  object 
of  the  whole  operation  is  achieved.  The  solution  is  then 
led  to  another  tank,  brought  up  to  its  proper  strength  again 
and  is  ready  to  be  used  once  more,  while  the  remains  of  the 
shavings  are  used  for  the  next  batch  of  material  to  be  treated. 

In  some  cases  the  crushed  ore  straight  from  the  crushing 
mill  is  cyanided,  in  others  it  is  simply  the  remains  left  over 
from  the  previous  amalgamating  process  which  is  thus 
treated.  All  depends  upon  the  nature  of  the  material  in 
question. 

There  are  other  chemical  methods  besides  the  cyaniding, 
but  it  is  the  chief.  It  has  been  found  specially  useful  with 
the  Johannesburg  ores,  and  to  it  the  South  African  goldfields 
owe  a  great  deal  of  their  success. 

There  is  a  more  modern  form  of  it,  although  the  whole 


120  GOLD  RECOVERY 

process  is  quite  novel,  having  been  introduced  only  in  the 
nineties  of  last  century.  This  development,  it  is  almost 
wearying  to  repeat,  is  electrical.  Instead  of  the  zinc  shav- 
ings being  used  to  precipitate  the  gold  out  of  the  solution,  the 
process  is  electrolytic.  A  lead  anode  is  used  while  the  process 
is  carried  on  in  a  box  the  bottom  of  which  is  covered  with 
mercury,  which  forms  the  cathode.  The  precipitated 
gold  is  thus  amalgamated,  the  amalgam  being  removed  at 
intervals,  retorted,  and  the  gold  recovered. 

The  idea  of  recovering  gold  from  the  waters  of  the  sea  is 
certainly  a  most  attractive  one.  To  some,  it  is  true,  the 
suggestion  may  bring  thoughts  the  reverse  of  pleasant,  for 
there  have  been  several  partially  successful  attempts  to 
delude  the  public  with  specious  promises  of  vast  dividends 
to  be  gathered  in  the  form  of  pure  gold  from  the  inexhaustible 
sea.  Still,  there  is  something  in  it,  and  some  day  the  dreams 
may  be  realised. 

The  quantity  of  gold  dissolved  in  sea-water  is  so  small 
that  in  200  cubic  centimetres  it  is  impossible  to  detect  it, 
even  by  the  most  delicate  tests  known.  The  quantity  needs 
to  be  multiplied  threefold  before  the  quantity  of  gold  becomes 
even  detectable,  to  say  nothing  of  being  recoverable. 

A  writer  in  Cassier's  Magazine,  a  few  years  ago,  related 
how  he  had  actually  obtained  gold  from  the  water  of  Long 
Island  Sound.  But  whereas  he  got  two  dollars'  worth,  it  cost 
him  over  4000  dollars  to  do  it.  No  company  will  ever  be 
floated  on  results  such  as  that.  From  the  mud  of  a  creek 
near  New  York,  however,  he  did  a  little  better,  for  there 
ten  dollars'  worth  of  gold  only  cost  379  dollars.  A  company 
promoter  would  still  look  askance  at  even  that  comparatively 
successful  undertaking. 

As  usual,  authorities  differ,  but  there  is  a  consensus  of 
opinion  that  in  every  ton  of  sea-water  there  is  from  one-half 
to  one  grain  of  gold,  besides  silver  and  iodine. 

It  seems  as  if  the  water  were  able  to  dissolve  that  amount 
and  no  more.  If,  as  has  been  suggested  earlier  in  this 
chapter,  all  the  gold  which  is  now  found  in  mines  and  in 


GOLD  RECOVERY  121 

gravel  beds  was  carried  there  in  water,  it  is  probable  that  the 
sea  obtains  its  gold  from  the  same  original  sources,  and  that, 
just  as  the  hot  ocean  of  ages  ago  carried  its  burden  of  gold 
in  solution,  so  the  colder  water  of  to-day  has  its  share,  the 
cold  water  naturally  carrying  less  than  the  hot  did. 

It  is  quite  likely,  then,  that,  could  we  find  out  how  to  rob 
the  sea  of  its  precious  metal,  it  could  replenish  its  store  from 
some  secret  hoard  of  its  own.  But  even  if  it  could  not,  it 
would  make  little  difference  to  us,  since  what  it  holds  is  far 
more  than  we  could  ever  use.  Put  it  at  half-a-grain  per  ton  : 
there  are  4205  million  tons  in  every  cubic  mile  of  ocean,  and 
300  million  cubic  miles  of  water  in  the  ocean.  If  all  the  gold 
that  man  has  ever  handled  were  to  be  dissolved  in  the  sea, 
no  chemist  would  be  able  to  discover  the  fact.  On  the  other 
hand,  if  that  half-grain  per  ton  which  we  believe  to  be  in  the 
ocean  now  were  to  be  recovered  we  should  have  about 
40,000  million  tons  of  gold,  a  prospect  which  is  enough  to 
make  the  political  economist  turn  pale  with  apprehension. 

What  is  required  is  some  substance  which,  on  being  added 
to  sea-water,  will  combine  with  the  gold,  and  then  be  pre- 
cipitated— that  is  to  say,  fall  to  the  bottom.  The  precipitate 
— that  which  falls  to  the  bottom — would  need  to  be  heavy,  so 
that  it  would  fall  quickly  and  not  necessitate  the  water  being 
left  standing  for  long  periods.  It  would  need  to  be  cheap, 
too,  or  easily  recoverable,  so  that  it  could  be  used  over  and 
over  again.  And,  finally,  it  would  need  to  be  such  that  the 
gold,  having  been  captured  by  it,  could  be  easily  obtained 
from  it. 

Given  such  a  precipitant,  the  process  of  recovering  the 
gold  would  be  simple  and  cheap.  Tanks  would  be  formed 
in  sheltered  bays  and  inlets.  At  every  tide  these  would  be 
filled,  and  when  full  the  precipitant  would  be  added.  The 
tide  falling,  the  water  would  run  out  again  and  leave  the 
precipitate  on  the  floor  of  the  tanks,  whence  it  could  be 
removed  by  scraping.  Simple  treatment  would  release  the 
gold  from  its  partner,  which  would  then  be  returned  to  the 
tanks  to  act  as  the  precipitant  once  more.  Thus  by  simple 


122  GOLD  RECOVERY 

means,  the  tide  itself  assisting,  the  gold  could  be  obtained 
from  the  sea. 

And  there  is  nothing  inherently  impossible  about  this 
suggestion.  The  necessary  precipitant  may  exist,  awaiting 
discovery.  A  large  works  operating  in  this  manner  would 
produce,  it  is  estimated,  about  thirteen  tons  of  gold  per 
annum.  It  looks  as  if  it  would  be  a  bad  day  for  the  Rand 
when  that  discovery  is  made. 

And  there  is  yet  another  possibility,  though  less  alluring 
than  what  has  just  been  described.  The  American  writer 
mentioned  a  little  while  back  got  a  better  return  from  the 
mud  of  a  creek  than  from  the  water  itself.  In  all  probability 
this  is  due  to  the  action  of  organic  matter  carried  down  by 
streams,  or  in  some  other  way  introduced  into  the  waters 
of  the  creek  whence  the  mud  was  obtained.  This  organic 
matter  would  possibly  have  an  effect  as  a  precipitant  upon 
the  dissolved  gold,  causing  it  to  be  thrown  out  of  solution 
and  deposited  in  the  mud.  Thus  the  mud  around  our  shores, 
and  particularly  in  the  creeks  and  estuaries,  may  be  potential 
gold  mines  whence  in  time  to  come  we  may  draw  supplies 
of  the  precious  metal.  The  cyanide  or  some  similar  process 
may  be  needed  in  order  that  we  may  extract  the  metal  from 
its  enclosing  mud,  but  the  time  may  not  be  so  very  far 
distant  when  dredging  for  gold  may  be  a  regular  occupation 
at,  for  example,  the  mouths  of  the  Thames  and  the  Hudson. 


CHAPTER   X 

INTENSE   HEAT 

MANY  of  the  useful  and  interesting  manufacturing 
processes  of  to-day  are  based  upon  the  intense 
heat  which  science  has  taught  the  manufacturer 
how  to  produce.     Tasks  which  our  forefathers  dreamed  of, 
but  were  unable  to  accomplish,  are  easy  to-day  because  of 
the  facility  with  which  great  heat  can  be  generated.     The 
"  burning  fiery  furnace  "  "seven  times  heated  "  is  as  nothing 
to  some  of  the  temperatures  which  are  now  obtained  in  the 
ordinary  course  of  things. 

The  greatest  heat  of  all  is  that  of  the  electric  arc.  Two 
conductors,  generally  rods  of  carbon,  are  placed  with  their 
ends  touching,  and  the  current  is  turned  on  so  that  it  passes 
from  one  to  the  other.  Then  they  are  gradually  drawn  apart. 
As  the  gap  widens  the  current  experiences  more  and  more 
difficulty  in  passing  over  this  non-conducting  gap,  and  great 
electrical  energy  has  to  be  employed  to  keep  it  going.  Now 
that  wonderful  law  of  the  Conservation  of  Energy  decrees 
that  no  energy  can  ever  be  lost.  It  can  only  be  changed 
from  one  form  into  another.  Therefore  the  energy  expended 
upon  the  arc  is  not  lost,  but  is  converted  into  heat.  It  is 
that  heat,  acting  upon  the  small  particles  of  carbon  which  are 
torn  off  the  ends  of  the  rods,  which  gives  us  the  arc  light. 

As  a  matter  of  fact  nearly  all  artificial  light  (and  natural 
light  too  for  that  matter1)  is  due  to  heat.  The  heat  sets 
the  molecules  in  violent  agitation,  which,  acting  upon  the 
corpuscles  in  the  atoms,  sets  them  in  violent  motion  too,  so 
that  light  is  often  the  companion  of  heat.  Some  substances 
give  light  more  readily  than  others,  under  the  influence  of 

1  The  glow-worm  is  an  example  of  the  few  exceptions. 
123 


124  INTENSE  HEAT 

heat,  and  we  may  reasonably  believe  that  they  are  those 
whose  corpuscular  arrangements  are  such  that  they  can  be 
readily  accelerated  by  the  molecular  action. 

To  take  a  familiar  instance,  coal-gas  is  mainly  "  methane," 
one  of  the  many  combinations  of  carbon  and  hydrogen,  and 
when  it  is  burnt  in  air  the  hydrogen  and  oxygen  combine, 
liberating  heat,  which  causes  the  carbon  liberated  at  the  same 
time  to  glow.  As  each  methane  molecule  breaks  up  the 
carbon  atoms  are  thrown  out,  forming  solid  particles  of 
carbon,  and  it  is  they  really  which  give  the  light.  It  is 
therefore  the  combustible  gas  heating  the  solid  particles 
of  carbon  which  forms  the  luminous  part  of  the  gas  flame. 
The  non-luminous  part  of  the  flame,  near  the  burner  (I  am 
now  speaking  of  the  old-fashioned  burner),  is  the  burning 
gas  before  the  carbon  particles  have  had  time  to  heat  up. 

And  the  old  gas  flame,  as  we  know,  is  now  being  rapidly 
displaced  by  the  incandescent  mantle,  the  reason  being 
simply  that  Von  Welsbach  discovered  how  certain  rare 
minerals  gave  a  more  brilliant  light  when  heated  than 
particles  of  carbon  do.  In  other  words,  it  is  easier  to 
accelerate  the  motion  of  the  corpuscles  in  ceria,  thoria 
and  the  other  ingredients  of  the  mantle,  than  it  is  those 
of  carbon.  Consequently,  they  sooner  reach  that  degree 
of  agitation  which  will  send  forth  electro-magnetic  waves  of 
the  high  frequency  necessary  to  produce  the  sensation  of 
light. 

For  this  reason  the  mantle  heated  by  gas  gives  as  bright 
a  light  as  the  carbon  particles  in  the  electric  arc,  although 
the  latter  are  subjected  to  a  much  more  intense  heat. 

But  the  arc  can  be,  and  often  is,  used  as  a  source  of  heat, 
apart  altogether  from  the  light  which  it  gives.  In  Sweden, 
for  example,  where  coal  is  rare,  but  water-power  plentiful, 
the  power  of  the  waterfalls  is  made  to  smelt  iron.  Hence  the 
waterfalls  are  sometimes  termed  the  "  white  coal "  of  that 
country.  Needless  to  say,  it  is  the  ubiquitous  electricity 
which  performs  the  change  from  the  force  of  falling  water 
into  heat. 


INTENSE  HEAT  125 

The  furnaces  are  in  shape  much  like  those  in  which  iron 
is  smelted  with  coal — namely,  tall  chimney-like  structures 
at  the  bottom  of  which  is  the  fire.  In  the  "  arc  furnaces  " 
there  are,  passing  in  through  the  side,  near  the  bottom,  a 
number  of  electrodes,  and  between  these  a  series  of  arcs  are 
formed.  Coke  and  ironstone  are  thrown  in  from  the  top 
into  this  region  of  intense  heat,  and  there  the  iron  is  liberated 
from  the  oxygen  with  which  it  is  combined  in  the  ore. 
Liberated,  it  flows  out  through  a  spout  at  one  side  of  the 
furnace. 

But  the  question  will  arise  in  the  reader's  mind :  Why  is 
coke  needed  in  an  electric  furnace  ?  It  is  for  metallurgical 
reasons.  The  heat  of  the  arc  loosens  the  bonds  between  the 
iron  and  oxygen,  but  it  needs  the  presence  of  some  carbon 
to  tempt  the  oxygen  atoms  away.  Therefore  coke,  as  the 
most  convenient  form  of  carbon,  has  to  be  there.  It  is 
there,  however,  in  much  smaller  quantity  than  it  would  be 
in  an  ordinary  furnace.  It  is  not  there  as  fuel,  but  simply 
as  the  "  counter-attraction "  to  draw  the  oxygen  atoms 
away  from  their  old  love. 

The  arc  is  also  used  for  welding  pieces  of  iron  together, 
for  which  purpose  it  is  eminently  suitable,  since  what  is 
wanted  is  intense  heat  at  a  particular  point.  But  perhaps 
the  reader  will  be  wondering  by  this  time  what  the  heat  of 
the  arc  is.  It  has  been  repeatedly  referred  to  as  "  intense," 
but  something  more  definite  may  be  demanded.  In  theory 
it  is  unlimited.  Apply  more  pressure — more  volts,  that  is — 
thereby  driving  more  current  across,  and  the  temperature 
will  rise.  It  is  only  a  question  of  making  dynamos  large 
enough,  and  driving  them  fast  enough,  and  any  temperature 
is  possible.  But  there  are  practical  difficulties  which  limit 
the  degree  of  heat.  One  is  the  melting-point  of  the  furnace 
itself.  Fire-clay  melts  at  about  1700°  to  1800°  C.  So  in  a 
furnace  which  has  to  be  lined  with  fire-clay  that  is  about  the 
limit. 

In  welding  two  pieces  of  iron  together,  the  iron,  of  course, 
defines  what  the  limit  shall  be.  It  needs  to  be  heated  to 


126  INTENSE  HEAT 

"  welding  heat "  and  no  more — that  is,  a  little  short  of 
melting — so  that  the  parts  to  be  joined  are  soft,  and,  with 
a  little  hammering,  will  join  thoroughly  together.  If  too 
much  heat  were  to  be  applied  the  parts  would  melt  away. 
But  the  heat  of  the  arc  can  be  controlled  by  simply  varying 
the  current,  and  so  the  right  heat  can  be  applied  at  the  right 
place,  than  which  little  more  is  wanted. 

One  very  simple  way  of  doing  this  is  for  the  workman 
to  hold  one  of  the  "  electrodes  " — a  rod  of  carbon  suitably 
insulated — in  his  hand.  The  current  is  led  to  it  through  a 
flexible  wire.  The  iron  itself  is  made  the  other  electrode 
by  being  gripped  in  a  vice  which  is  itself  insulated  but  con- 
nected to  the  source  of  current.  Thus  on  bringing  the  point 
of  his  rod  near  to  the  part  to  be  heated  the  man  causes  an 
arc  to  be  created  there.  By  moving  the  rod  he  can  move 
the  arc  about,  heating  one  part  more  than  another,  distribut- 
ing his  heat  if  he  wants  to  do  so  over  a  larger  area,  or  keeping 
it  to  a  small  one,  just  as  he  wills.  On  reaching  the  right  heat 
the  rod  is  withdrawn,  the  arc  destroyed,  and  the  iron  can  be 
hammered  just  as  if  it  had  been  heated  in  a  fire. 

Yet  another  way  still  is  known  as  "  resistance  "  welding. 
In  it  an  enormous  current  at  an  extremely  low  voltage  is 
used.  The  fundamental  principle  is  the  same,  since  the 
heat  is  formed  by  forcing  current  past  a  point  over  which 
it  is  reluctant  to  pass.  That  point  of  poor  conductivity 
is  the  ends  of  the  two  bars  to  be  joined.  They  are  placed 
just  touching,  but  since  an  imperfect  contact  like  that  always 
offers  considerable  resistance  to  the  flow  of  a  current,  the 
passing  current  needs  only  to  be  made  large  enough  for  great 
heat  to  be  generated. 

This  is  exceedingly  pretty  to  watch.  We  will  suppose 
that  the  article  to  be  operated  upon  is  the  tyre  of  a  wheel. 
The  bar  of  iron  has  already  been  bent  by  rollers  into  the 
correct  curve  and  the  two  ends  are  touching.  Brought  to 
the  machine,  it  is  gripped,  each  side  of  the  junction,  in  the 
jaws  of  an  insulated  vice  and  the  current  is  turned  on.  In 
a  few  seconds  the  place  where  the  two  ends  are  just  touching 


INTENSE  HEAT  127 

begins  to  glow.  Rapidly  it  increases  in  brightness  until 
in  about  half-a-minute  it  is  at  welding  heat.  Then  one  vice, 
which  is  movable,  is  forced  along  a  little  by  a  screw,  so  that 
the  ends  are  pressed  firmly  together,  a  little  judicious 
hammering  meanwhile  helping  to  complete  the  job.  Then 
the  current  is  switched  off  and  the  complete  tyre  taken  out 
of  the  machine.  The  current  used  has  a  force  comparable 
with  that  which  operates  domestic  electric  bells,  but  in 
volume  it  is  thousands  of  amperes.  Alternating  current  is 
used,  and  it  is  obtained  from  a  transformer  or  induction  coil. 
In  such  a  case  the  primary  part  of  the  coil  is  made  of  many 
turns  of  fine  wire,  so  that  little  current  passes  through  it, 
while  the  secondary  part  is  but  one  or  two  turns  of  thick  bar. 
Thus  the  voltage  generated  in  the  secondary  is  very  little, 
but  since  the  secondary  has  an  almost  negligible  resistance 
the  current  caused  by  that  small  voltage  is  enormous.  Such 
an  arrangement  is  in  industrial  realms  generally  called  a 
transformer,  the  term  induction  coil  being  employed  more 
for  those  things  of  a  similar  nature  intended  for  the  laboratory. 
The  one  just  described  is,  moreover,  a  "  step-down  "  trans- 
former, since  it  lowers  the  voltage,  to  distinguish  it  from 
"  step-up  "  transformers,  which  raise  the  voltage. 

And  the  "  resistance  "  principle  is  also  applied  in  another 
way  to  large  furnaces,  such  as  those  for  refining  iron.  In 
these  the  resistance  of  the  iron  itself  is  utilised  to  generate 
the  heat.  Of  course,  it  should  be  well  understood,  heat  is 
always  generated  in  everything  through  which  current  flows. 
There  is  no  perfect  conductor,  and  so  every  conductor  is 
more  or  less  heated  by  the  passage  of  current  through  it. 
Some  energy  needs  to  be  expended  to  drive  current,  even  along 
large  copper  wires,  and  that  energy  must  be  turned  into 
heat  in  the  wires.  If  the  same  volume  of  current  be  forced 
along  iron  wires  of  the  same  size,  the  heat  will  be  greater, 
since  iron  is  but  a  poor  conductor  compared  with  copper, 
the  relation  being  about  as  one  to  six.  And  if  the  iron  be 
hot  the  resistance  will  be  still  more,  for  it  stands  to  reason 
that  when  heated  the  molecules,  being  farther  apart,  will 


128  INTENSE  HEAT 

be  the  less  easily  able  to  exchange  corpuscles.  We  have  the 
best  reasons  for  believing,  as  has  been  suggested  already,  that 
a  current  of  electricity  is  but  a  flow  of  corpuscles,  and  so  we 
are  not  surprised  to  hear  that,  as  a  general  rule,  the  hotter 
a  thing  is  the  less  does  it  conduct  electricity. 

So  imagine  a  circular  trough  of  fire-clay  or  other  heat- 
resisting  material  filled  with  fragments  of  iron,  or,  it  may  be, 
with  iron  barely  above  melting-point,  which  has  come  from 
another  furnace,  where  it  underwent  the  previous  process. 
Circling  inside  or  outside  this  trough  is  an  enormous  coil  of 
wire  through  which  currents  of  electricity  are  alternating. 
That  is  the  "  primary "  of  a  transformer,  and  the 
"  secondary  "  is — the  iron  itself,  in  the  trough.  If  it  be, 
as  it  often  is,  in  the  form  of  scrap,  or  broken  pieces,  the  heat 
will  begin  to  show  itself  where  the  pieces  touch  each  other. 
The  currents  generated  in  the  trough,  by  the  coil  outside, 
will,  of  course,  pass  from  piece  to  piece  and  the  points  of 
contact,  since  they  offer  the  greatest  resistance,  will  show 
signs  of  heat.  This  will  increase  until  the  pieces  begin  to 
melt.  As  the  separate  fragments  merge  into  the  molten 
mass  the  resistance  will  in  one  way  decrease,  for  the  im- 
perfect contacts  between  the  pieces  will  give  place  to  the 
perfect  contact  throughout  the  mass  of  liquid  metal.  But 
for  another  reason — namely,  the  increase  in  heat — the  resist- 
ance will  increase.  And  all  the  while  the  alternations  in  the 
primary  coil  will  be  pumping  currents,  as  it  were,  round  and 
round  the  ring  of  molten  iron.  Whether  the  resistance 
increase  or  decrease,  the  current  will  do  the  opposite,  so  that 
heat  will  be  generated  whatever  happens.  For  as  resistance 
decreases  current  increases,  and  vice  versa.  And  the  slightest 
variation  in  the  strength  of  the  primary  current  will  have  its 
effect  upon  the  secondary,  and  therefore  on  the  heat  gener- 
ated. So,  by  simply  regulating  the  primary  current,  the 
temperature  of  the  metal  can  be  controlled  to  a  nicety. 
And  such  furnaces  have  the  immense  advantage  that  there 
is  no  possibility  of  deleterious  substances  in  the  fuel  getting 
into  and  spoiling  the  metal,  a  thing  which  may  very  easily 


v permission  ojf  Cambridge  Scientific  Inst.  Co.,  Ltd.,  Cambridge,  Eng. 

MEASURING  HI<:AT  AT  A  DISTANCE 

This  wonderful  instrument,  the  Fery  Radiation  Pyrometer,  although  itself 
some  distance  away  from  the  furnace,  is  telling  the  temperature  of  its 
hottest  part 


INTENSE  HEAT  129 

happen  during  the  manufacture  of  high-class  steels,  alloys 
of  iron  in  which  the  exact  quantities,  purity  and  proportions 
of  the  ingredients  are  of  the  utmost  importance. 

Hence  these  "  induction  furnaces,"  as  they  are  called,  are 
frequently  used  quite  apart  from  any  question  of  utilising 
water-power.  And  they  will  probably  be  used  still  more 
as  time  goes  on. 

For  one  thing,  they  may  become  valuable  adjuncts  to  the 
older  form  of  iron  and  steel  furnaces,  from  which  they  will 
obtain  their  power  free,  gratis  and  for  nothing.  In  districts 
such  as  Middlesbrough  they  could  generate  more  electricity 
than  they  have  any  use  for.  The  ordinary  iron  furnaces 
belch  forth  flames  which  are  really  good  useful  gas  (carbon 
monoxide)  burning  to  waste.  Many  of  the  furnaces  are 
covered  in  at  the  top,  and  this  gas  is  led  away  to  heat 
boilers  for  the  steam-engines  or  to  drive  large  gas-engines, 
but  in  a  large  works  there  is  more  of  this  waste  gas  than 
they  know  what  to  do  with.  Now  that  could,  and  probably 
will  ere  long,  be  turned  into  electricity  by  means  of  gas- 
engines  and  the  current  used  for  making  steel  in  induction 
furnaces. 

It  will  probably  surprise  many  to  know  that  these  enor- 
mous currents  which  can  thus  heat  great  masses  of  metal 
until  they  melt  are  no  danger  at  all  to  the  men  who  work 
with  them.  A  man  might  dip  an  iron  rod  into  the  trough 
of  metal  and  he  would  scarcely  feel  the  shock.  And  the 
same  is  true  of  the  welding  machine,  which  can  be  touched 
in  any  part  without  fear.  The  reason,  of  course,  is  that, 
broadly  speaking,  it  is  volume  of  current  which  does  harm, 
and  the  resistance  of  the  human  body  is  so  great  that  with 
the  small  voltages  used,  the  volume  which  can  pass  is 
negligible.  It  should  be  mentioned,  however,  that  the 
volume  of  current  in  lightning  is  also  small,  but  we  know 
that  it  is  capable  of  inflicting  terrible  injury.  Lightning, 
however,  is  in  a  class  by  itself.  Our  terrestrial  voltages 
are  baffled  by  an  air-gap  of  a  few  inches,  but  lightning 
springs  across  a  gap  miles  wide.  Its  voltage  must, 


130  INTENSE  HEAT 

therefore,  amount  to  millions,  and  the  ordinary  rules  relating 
to  earthly  currents  do  not  apply. 

But  other  sources  of  heat  besides  electricity  are  at  the 
disposal  of  our  manufacturers  nowadays.  Pre-eminently 
there  is  the  flame  of  some  gas  burning  with  pure  oxygen. 
The  oxyhydrogen  jet  has  been  known  for  many  years  as  the 
best  means  of  producing  the  light  for  a  magic  lantern.  Such 
a  jet  impinging  upon  a  pencil  of  lime  causes  the  latter  to 
glow  with  a  dazzling  white  light. 

But  the  oxyhydrogen  jet  is  now  employed  in  many 
factories  for  the  welding  of  metals.  This  is  known  as  fusion 
welding,  since  the  two  parts  are  actually  reduced  to  liquid. 
The  usual  way  to  go  about  this  work  is  to  bevel  off  the  ends 
or  edges  to  be  joined.  Suppose,  for  instance,  that  we  wanted 
to  weld  two  pieces  of  brass  pipe  together.  We  should  first 
file  or  otherwise  trim  the  edges  to  be  joined  until  when  put 
together  they  form  a  groove  practically  as  deep  as  the 
metal  is  thick.  Then  with  a  stick  of  brass  wire  in  the  left 
hand,  and  an  oxyhydrogen  blowpipe  in  the  right,  we  should 
direct  the  flame  from  the  pipe  on  to  the  metal  until,  at  one 
point,  the  sides  of  the  groove  were  beginning  to  melt.  Then, 
inserting  the  point  of  the  wire  into  the  groove,  we  should 
melt  a  little  off  it.  Thus  we  should  work  all  round  the  joint, 
melting  the  sides  of  the  groove  and  filling  in  with  melted 
metal  from  the  wire,  until  the  whole  groove  had  been  filled 
up  and  the  metal  added  had  been  thoroughly  amalgamated 
with  that  on  either  side. 

As  a  matter  of  fact,  if  it  were  brass  which  we  were  working 
on  we  should  probably  use  the  cheaper  though  less  pure 
form  of  hydrogen — coal-gas — so  that  it  would  really  be 
*'  oxycoal-gas  "  that  we  should  use  and  not  oxyhydrogen. 
The  latter  is  used,  however,  notably  for  the  fusion-welding 
of  lead,  or  "  lead-burning,"  as  it  is  termed. 

The  blowpipe  is  a  brass  tube  about  a  foot  or  eighteen  inches 
long,  with  two  passages  in  it,  one  for  the  oxygen  and  the 
other  for  the  other  gas.  The  gases  are  brought  to  one  end 
of  it  through  rubber  pipes,  while  at  the  other  end  there  is 


INTENSE  HEAT  181 

a  nozzle  in  which  the  gases  mingle  and  from  which  they 
emerge  in  a  fine  jet. 

The  oxyhydrogen  flame  has  a  temperature  of  about  2000°  C., 
hot  enough  to  melt  fire-clay.  That  does  not  matter  in  the 
case  of  welding,  however,  since  the  molten  metal  is  very 
small  in  quantity  at  any  given  moment,  and  is  allowed  to 
cool  before  it  can  run  away.  It  would  be  an  awkward 
temperature  to  deal  with,  nevertheless,  in  a  furnace.  It 
seems  strange  that  it  does  not  burn  the  nozzle  of  the  blow- 
pipe, but  the  fact  that  it  does  not  is,  it  is  believed,  explained 
by  the  fact  that  the  expansion  of  the  gas,  as  soon  as  it  emerges 
from  the  hole  out  of  which  it  shoots,  causes  a  comparatively 
cool  space  just  there,  shielding  it  from  the  intense  heat 
farther  on. 

An  exceedingly  interesting  use  of  the  oxyhydrogen  flame 
is  in  the  manufacture  of  artificial  rubies.  These  stones  are 
made  in  Paris  by  a  very  simple  means.  The  necessary 
chemicals  are  prepared  and  ground  to  an  exceedingly  fine 
powder.  This  is  then  allowed  to  fall  through  an  oxyhydrogen 
flame.  Thus  there  is  no  need  for  a  crucible  capable  of 
withstanding  this  high  temperature,  since  the  melting  takes 
place  as  the  particles  are  in  the  act  of  falling.  When  they 
reach  the  support  prepared  to  catch  them  they  have  cooled 
somewhat.  Stones  so  called  are  real  rubies — artificial,  but 
not  shams.  They  possess  every  property  of  the  ruby  from 
the  mine. 

Another  product  of  the  oxyhydrogen  flame  is  the  quartz 
fibres  which  are  used  for  suspending  the  needles  in  the  finest 
galvanometers.  The  quartz  is  melted,  in  this  case  a  crucible 
being  employed.  An  arrow  is  then  dipped  in  the  liquid 
quartz  and  immediately  "fired"  into  the  air.  The  thick 
treacly  liquid  is  thus  drawn  out  into  a  thread  of  such  fineness 
that  a  microscope  is  necessary  to  find  it  with. 

Hotter  even  than  oxyhydrogen  is  the  oxyacetylene  flame, 
which  at  its  hottest  point  reaches  nearly  3500°  C. 
The  gas,  which  is  another  of  the  combinations  of  carbon  and 
hydrogen  (its  molecules  containing  two  atoms  of  each),  is 


132  INTENSE  HEAT 

easily  made  by  allowing  water  to  come  into  contact  with 
calcium  carbide.  The  latter,  which  is  CaC2,  is  made  by 
heating  coke  and  lime  together  in  the  intense  heat  of  an 
electric  furnace.  This  accounts  largely  for  the  great  heating 
power  of  acetylene,  for  since  great  heat  is  necessary  to  cause 
the  elements  to  combine  great  heat  is  given  out  by  them 
when  they  ultimately  separate.  Here  again  is  the  conserva- 
tion of  energy.  The  heat  energy  of  the  electric  furnace  is 
largely  expended  in  forcing  these  two  elements  into  partner- 
ship. They  are,  as  it  were,  given  a  large  amount  of  capital 
in  the  form  of  heat.  It  ceases  to  be  sensible  heat,  becoming 
latent  in  the  compound,  but  still  it  is  there.  So  a  lump  of 
calcium  carbide,  with  which  many  readers  are  familiar,  has 
vast  stores  of  heat  locked  up  within  it.  When  water  comes 
into  contact  with  the  carbide  the  partnership  is  broken, 
but  the  heat  is  not  liberated  then,  since  another  partnership 
is  formed,  which  still  retains  the  old  heat-capital.  The  calcium 
in  the  carbide  is  displaced  by  the  hydrogen  from  the  water, 
and  so  C2H2  comes  into  being,  while  the  rejected  calcium 
consoles  itself  by  entering  into  combination  with  the  equally 
forsaken  oxygen  from  the  water,  forming  CaO,  which  is 
but  another  name  for  lime. 

Then  the  acetylene  (C2H2)  is  mixed  with  oxygen  in  the 
blowpipe  and  burnt,  under  which  conditions  the  pent-up 
heat,  borrowed  originally  from  the  electric  furnace,  is  brought 
into  play.  With  this  flame  the  harder  metals  can  be  fused 
and  welded.  Wrought  iron,  cast  iron,  steel  in  all  its  forms, 
all  can  be  melted  by  the  oxyacetylene  flame,  almost  as  easily 
as  snow  by  a  hot  iron.  The  fusion  welding  of  these  metals 
is  then  carried  on  just  as  already  described  for  brass. 

By  means  of  a  special  blowpipe,  wherein  an  excess  of 
oxygen  is  introduced  at  the  hot  point,  hard  steel  plates  can 
be  cut  to  pieces  almost  as  easily  as  a  grocer  cuts  cheese. 
Even  thick,  hard  armour-plate  can  thus  be  cut,  almost  the 
only  way,  indeed,  in  which  it  can  be  cut. 

And  for  purposes  such  as  welding  and  cutting  this  flame 
has  an  interesting  and  peculiar  advantage  over  all  other 


INTENSE  HEAT  188 

kinds  of  heat.  When  a  metal  is  heated  in  the  air  there  is 
usually  trouble  from  oxidation.  The  domestic  poker,  for 
example,  after  it  has  been  left  to  get  red-hot  in  the  fire  is 
seen  to  be  coated,  in  the  part  which  has  been  heated,  with 
scales  which  will  flake  off  if  the  thing  be  struck.  Those  scales 
are  oxide  of  iron,  caused  by  the  union  of  iron  and  oxygen 
when  the  poker  was  hot.  But  if  the  heat  be  applied  by  the 
oxyacetylene  flame  that  will  not  happen.  The  oxygen  and 
the  carbon  from  the  acetylene  will  burn,  and  if  the  supply 
of  the  former  be  properly  regulated  it  will  be  entirely  used 
up  in  the  process.  The  hydrogen  from  the  acetylene  is, 
strange  to  say,  unable  to  unite  with  oxygen  at  such  a  high 
temperature  as  that  of  the  oxygen  and  carbon,  so  that  it 
passes  on  beyond  the  oxygen-carbon  flame  and  ultimately 
burns  on  its  own  account  with  the  oxygen  from  the  atmos- 
phere in  a  second  flame  surrounding  the  first.  Thus  there 
is  a  double  flame :  inside,  a  little  pointed  cone  of  white 
flame,  that  is  the  oxygen  and  carbon ;  and  outside  that  a 
bluish  flame,  the  hydrogen  and  the  atmospheric  oxygen. 
The  latter  flame  forms  a  kind  of  jacket  entirely  enveloping 
the  former.  And  so  when  one  melts  metal  by  means  of  the 
white  cone  the  hydrogen  jacket  shields  the  molten  metal 
from  oxygen  and  prevents  the  oxidation.  Only  one  who 
knows  the  bother  caused  by  oxidation  whenever  metals  are 
heated  can  realise  the  wonderful  advantage  of  this. 

And  now  we  can  turn  to  even  another  source,  also  quite 
modern,  of  high  temperature. 

If  the  oft-quoted  "  man  in  the  street  "  were  asked  the  two 
commonest  things  on  earth  he  might  possibly  name  oxygen 
as  one,  and  so  far  he  would  be  right,  but  the  chances  are 
much  against  his  naming  aluminium  as  the  second.  If  he 
did  not,  however,  he  would  be  wrong.  Aluminium  and 
oxygen  form  alumina,  of  which  are  constituted  the  sapphire, 
the  ruby  and  other  precious  stones,  but  alumina  is  most 
commonly  found  in  combination  with  silica,  or  silicon  and 
oxygen.  This  compound  is  called  silicate  of  aluminium,  and 
of  it  are  formed  clay  and  many  rocks.  The  reason  why  the 


184  INTENSE  HEAT 

metal  aluminium  was  until  recently  rare  and  expensive 
was  because  of  the  great  difficulty  of  disentangling  the  metal 
from  this  rather  complex  combination.  And  these  two 
commonest  elements  have,  under  certain  conditions,  a  rare 
affinity  for  each  other.  They  join  forces  with  such  energy 
that  great  heat  is  given  out  in  the  process.  This,  again, 
we  may  regard  as  an  example  of  the  conservation  of  energy. 
Heat  had  to  be  used  up,  apparently,  in  separating  the 
aluminium  and  oxygen  as  they  were  found  together  in  the 
natural  state.  And  that  heat  reappears  when  they  combine 
together  again.  This  is  a  most  useful  principle,  for  if  heat 
has  disappeared  anywhere  in  the  course  of  some  operation, 
we  know  that  in  all  probability,  if  we  go  about  it  the  right 
way,  we  can  get  that  heat  back  again,  perhaps  in  a  more 
convenient  form.  That  is  so  in  this  case  at  all  events. 

Now  aluminium  will  not  readily  combine  with  atmospheric 
oxygen,  but  it  will  readily  do  so  with  oxygen  from  the  oxide 
of  a  metal.  So  if  we  put  into  a  vessel  some  oxide  of  iron 
and  some  finely  powdered  aluminium,  and  give  it  some  heat 
at  one  point,  just  to  set  the  process  going,  the  whole  mass  will 
burn  with  intense  heat.  And  when  the  burning  is  finished 
the  crucible  will  be  found  to  contain  (1)  some  molten  iron, 
the  oxide  of  iron  with  the  oxygen  gone,  and  (2)  some  oxide 
of  aluminium  or  alumina,  in  the  form  which  we  call  corundum, 
a  very  hard  substance  which  in  a  powdered  form  is  used  for 
grinding  hard  metals.  We  start,  you  will  notice,  with  a  pure 
metal  and  an  oxide.  We  finish  with  a  pure  metal  and  an 
oxide,  only  the  oxygen  has  changed  its  quarters,  having 
passed  from  the  iron  to  the  aluminium.  And  in  the  course 
of  the  change  a  vast  amount  of  pent-up  heat  has  been 
liberated.  Aluminium  is  thus  a  fuel,  strange  though  it  may 
seem  to  say  so,  just  as  coal  is.  Coal,  however,  is  willing  to 
pair  off  with  oxygen  from  the  air,  while  aluminium,  more 
fastidious,  will  only  accept  it  as  partner  when  it  can  steal 
it  from  another  combination. 

But  the  practical  result  is  eminently  satisfactory,  for  the 
action  of  the  aluminium  and  iron  oxide  is  to  leave  us  with  a 


INTENSE  HEAT  185 

crucible  full  of  molten  iron  at  a  very  high  temperature. 
And  this  can  be  used  in  various  ways. 

Tramway  rails,  for  example,  can  be  joined  together  by  it. 
A  mould  is  formed  around  the  ends  of  two  rails,  where  they 
"  butt "  together,  and  into  this  mould  a  quantity  of  the 
melted  iron  can  be  poured.  So  hot  is  it  that  it  partially 
melts  the  ends  of  the  rails,  and  then,  amalgamating  with 
them,  it  forms  a  perfectly  homogeneous  connection  between 
them. 

The  same  method  can  be  applied  to  the  repair  of  iron 
structures  of  all  kinds.  The  propeller  shaft  of  a  ship,  for 
example,  sometimes  breaks  on  a  voyage.  Such  a  catastrophe 
is  fraught  with  the  most  serious  consequences,  unless  it  can 
be  quickly  repaired.  Thermit,  as  this  process  is  called,  is 
perhaps  the  only  means  whereby,  under  certain  conditions, 
this  can  be  accomplished. 

The  extraordinary  heat  of  the  metal  produced  in  this  way 
is  demonstrated  by  the  fact  that  if  it  be  poured  on  to  an  iron 
plate  an  inch  thick  it  goes  clean  through  it.  It  melts  its 
way  through  instantly. 

But  although  such  high  temperatures  are  at  the  command 
of  the  modern  manufacturer,  there  are  some  things — indeed 
many  things — which  still  baffle  him,  the  diamond,  for 
example.  It  is  true  that  diamonds  of  small  size  have  been 
made,  but  larger  ones  have  so  far  defied  all  efforts. 

One  very  interesting  fact  about  this  may  be  mentioned 
in  concluding  this  chapter.  Sir  Andrew  Noble,  a  member 
of  the  great  firm  of  Armstrong,  Whitworth  &  Co.,  of  Elswick, 
tried  the  experiment  of  exploding  some  cordite,  a  high 
explosive,  inside  a  steel  vessel  of  enormous  strength.  He 
thus  produced  what  is  believed  to  be  the  highest  tempera- 
ture ever  produced  on  earth.  It  is  reckoned  to  have 
been  5200°  C.,  and  the  pressure  at  the  same  time  was, 
it  is  calculated,  50  tons  per  square  inch.  His  intention  was 
not  to  make  diamonds,  but  Sir  William  Crookes  predicted 
that  diamonds  would  be  the  result.  For  the  cordite  con- 
sisted mainly  of  carbon,  which,  as  is  well  known,  is  the 


136  INTENSE  HEAT 

material  of  which  the  diamond  is  formed,  and  the  combina- 
tion of  high  temperature  and  high  pressure  is  just  what  is 
needed,  so  it  is  believed,  to  bring  the  carbon  into  this  par- 
ticular form.  And  true  enough,  on  the  iron  being  examined 
after  the  explosion,  there  were  seen  tiny  diamonds.  For 
larger  ones  even  higher  temperatures  and  greater  pressures 
are,  no  doubt,  necessary,  and  as  the  diamond,  like  gold,  has 
a  peculiar  fascination  for  mankind,  so  the  efforts  to  manu- 
facture it  will  continue.  In  years  to  come  the  means  may 
be  found  of  creating  these  extreme  conditions  of  temperature 
and  pressure,  and  so  another  of  the  problems  of  the  ages 
will  be  solved. 


Ky  permission  oj  tne  British.  Aluminium  Co 

A  STRIKING  FEATURE  OF  MODERN  ALUMINIUM  WORKS 

For  the  production  of  aluminium  water  power  is  required.  Water  is  stored  at  a  high 
level  and  is  then  brought  down  to  the  factory  in  pipes.  The  illustration  shows  the  pipe 
track  recently  laid  do.vn  for  this  purpose  at  Kinlochleven  in  Argyleshire.  The  six  pipes, 
each  of  which  is  thirty-nine  inches  in  diameter,  run  down  the  hillsides  for  one  mile  and 
a  quarter 


CHAPTER  XI 

AN   ARTIFICIAL  COAL   MINE 

THOSE  countries  which  are  blessed  with  a  plentiful 
supply  of  coal  are  periodically  shocked  and  saddened 
by  a  terrible  calamity — an  explosion  in  one  of  the 
mines,  in  which  often  scores  of  poor  fellows  lose  their  lives, 
and  hundreds  of  widows  and  orphans  find  themselves  without 
a  breadwinner.  One  has  only  to  recall  that  heart-rending 
calamity  of  the  Courrieres  mines  in  France,  where  over  a 
thousand  lives  were  lost,  to  realise  how  important  is  the 
question  of  the  cause  and  the  cure  of  the  colliery  explosion. 
It  used  to  be  thought  a  settled  matter  that  these  were  due 
to  the  accidental  ignition  of  a  gas  called,  scientifically, 
"methane,"  but  by  the  miners  "fire-damp."  This  un- 
doubtedly does  collect  in  many  mines,  and  since  it  is  much 
the  same  as  the  domestic  coal-gas  (indeed  methane  forms  the 
bulk  of  coal-gas)  it  is  not  surprising  that  the  explosions  were 
attributed  to  it.  At  times  shots  were  fired,  to  blast  down 
the  coal,  and  although  the  greatest  precautions  are  taken 
to  prevent  any  accident  resulting,  it  seems  certain  that 
explosions  have  occasionally  followed  the  firing  of  shots. 
But  still  more  dangerous  is  the  adventurous  miner  who, 
for  some  reason,  opens  his  safety  lamp.  It  is  lit  for  him 
before  he  enters  the  workings,  and  locked  up,  so  that,  theo- 
retically, he  cannot  tamper  with  it ;  but  it  has  to  be  a  cleverly 
devised  lock  that  cannot  be  picked  in  some  way,  and  with 
the  carelessness  born  of  long  immunity  from  accident  these 
are  got  open  sometimes,  with,  it  may  be,  disastrous  results. 
Even  a  spark  struck  from  a  miner's  pick  may  ignite  the 
gas ;  or  a  spark  from  some  electrical  machine  used  in  the 
mine.  That  is  one  of  the  reasons  why  electrical  apparatus 

137 


138  AN  ARTIFICIAL  COAL  MINE 

is  suspect  in  colliery  matters  and  machines  worked  by  the 
less  convenient  and  more  costly  means  of  compressed  air 
are  preferred. 

In  some  such  manner  the  fire-damp  is  ignited,  and  then 
there  follows  the  fiery  blast,  which,  sweeping  through  the 
narrow  galleries  and  passages  which  constitute  the  workings, 
simply  licks  up  the  life  of  the  men  whom  it  encounters. 
Others,  in  byways  and  sheltered  corners,  escaping  the 
burning  cloud  of  flame,  are  poisoned  by  the  deadly  fumes 
of  carbon  monoxide  which  it  leaves  when  its  force  is  spent. 
While  others,  perchance  the  most  unfortunate  of  all,  are 
saved  for  a  time,  but,  being  imprisoned  by  falls  from  the 
roof  and  walls,  die  a  lingering  death  of  hunger  and  slow 
suffocation.  A  colliery  explosion  is  one  of  the  ghastliest 
events  imaginable,  the  only  relief  from  which  is  the  noble 
heroism  with  which  the  survivors,  from  the  mine  managers 
to  the  humblest  workmen,  crowd  round  the  pit-mouth,  eager 
to  risk  their  own  lives  for  the  faint  chance  of  saving  some 
below.  Not  infrequently  these  brave  volunteers  only  share 
the  fate  of  the  men  they  would  rescue. 

Now  all  that,  as  I  have  said,  used  to  be  put  down  to  the 
effect  of  the  fire-damp.  But  it  dawned  upon  men's  minds 
some  years  ago  that  the  damage  seemed  to  be  out  of  pro- 
portion to  the  power  of  the  gas.  Modern  mines  are  well 
ventilated  by  large  fans,  which  impel  great  volumes  of  air 
through  all  the  workings.  The  air  currents  are  cunningly 
guided  by  partitions  or  "  brattices,"  so  that  every  nook  and 
corner  shall  be  scoured  out  by  the  plentiful  draught  of  pure 
fresh  air.  Consequently  the  amount  of  explosive  gas  which 
can  collect  in  any  one  place  is  but  small.  How,  then,  can  so 
small  a  volume  of  gas  do  so  large  an  amount  of  damage  ? 

Coupled  with  this  was  the  fact  that  explosions  take  place 
in  flour  mills,  where  there  is  no  gas,  and  experimenters  had 
found  in  their  laboratories  that  almost  any  burnable  sub- 
stance, if  ground  up  finely  enough  and  blown  into  a  cloud, 
would  explode.  Coal-dust  would  naturally  do  this.  Indeed 
anyone  throwing  the  dust  from  the  bottom  of  the  coal- 


AN  ARTIFICIAL  COAL  MINE  189 

shovel  upon  a  fire  will  see  for  himself  how,  quickly  such  dust 
will  burn,  and,  as  has  been  pointed  out  in  an  earlier  chapter, 
an  explosion  is  but  rapid  burning. 

So  the  blame  was  largely  transferred  from  the  shoulders 
of  the  fire-damp  to  those  of  the  clouds  of  coal-dust  which 
collect  throughout  the  workings  of  a  mine. 

But  then  a  difficulty  arose  from  the  fact  that  there  is  dust 
in  all  mines,  yet  some  districts  are  quite  free  from  explosions. 
And  such  districts  are  those  where  there  is  little  or  no  fire- 
damp. These  two  facts  seem  to  be  explainable  in  one  way, 
and  in  one  way  only.  It  must  be  that  the  gas  first  of  all 
explodes  feebly,  and  so,  stirring  up  the  dust  lying  along  the 
roads  and  passages,  prepares  the  way  for  the  powerful, 
deadly  explosion  of  coal-dust  which  follows. 

But  that  was  only  a  guess,  and  the  matter  was  of  such 
importance  that  it  needed  something  more  certain  than 
mere  assumption.  So  the  Mining  Association  of  Great 
Britain  decided  to  have  a  series  of  experiments  which  should 
settle  once  and  for  all  what  part  the  coal-dust  played  in 
these  catastrophes,  and  how  best  they  could  be  prevented. 

It  was  at  first  thought  that  an  old  mine  might  be  utilised 
for  the  experiments,  but  there  was  the  difficulty  that  such 
always  become  wet  after  work  has  ceased  in  them,  and  so 
the  dust  would  not  behave  normally.  Moreover,  the  work 
would  be  extremely  dangerous  and  the  results  difficult  to 
observe.  Then  a  culvert  was  suggested  built  of  concrete, 
partly  buried  in  the  ground,  but  that  too  was  dismissed. 
Finally  it  was  decided  to  make  an  imitation  mine  of  steel, 
using  old  boiler  shells  with  the  ends  taken  out. 

The  sum  of  £10,000  was  subscribed  for  the  purpose  by  the 
coal-owners  of  Great  Britain,  and  the  great  work  was  carried 
out  at  Altofts,  in  Yorkshire,  close  to  a  colliery  where  a  terrible 
disaster  occurred  in  1886. 

Here  the  great  tube  or  gallery  was  built.  Roughly  the 
shape  of  a  letter  L,  one  leg  is  over  1000  feet  long,  while  the 
other  is  295  feet.  The  longer  leg  is  7|  feet  in  diameter  and 
the  shorter  6  feet.  At  the  end  of  the  shorter  part  a  large 


140  AN  ARTIFICIAL  COAL  MINE 

fan  is  installed  which  can  force  50,000  to  80,000  cubic  feet 
of  air  per  minute  through  the  structure,  so  producing  the 
conditions  of  a  well-ventilated  mine.  The  shorter  length 
has  several  sharp  turns  in  it  for  the  purpose  of  breaking  the 
force  of  the  explosion  along  that  part,  and  so  shielding  the 
fan  from  damage,  wnile  a  tall  chimney  is  provided  there, 
so  that,  the  door  being  shut  to  cut  off  the  fan,  the  gases 
from  the  explosion  can  find  a  harmless  way  out. 

Inside  the  tube,  shelves  are  fixed  along  the  sides  so  as  to 
reproduce  the  effect  of  the  timbering  in  a  real  mine,  upon  the 
beams  of  which  the  dust  finds  lodgment.  Props  were  put 
up  too,  just  as  they  would  be  in  the  real  mine.  Everything, 
in  fact,  was  done  to  make  the  place  as  perfect  a  replica  as 
possible  of  actual  underground  workings. 

And  then,  added  to  this  huge  and  costly  structure,  was 
an  outfit  of  scientific  instruments  worthy  of  the  important 
investigations  which  were  to  be  carried  on. 

To  grasp  the  purpose  and  working  of  these  we  need  to 
remind  ourselves  of  the  aims  and  intentions  of  the  experi- 
ments. First  of  all  it  was  desired  to  find  out  how  various 
quantities  and  qualities  of  coal-dust  behaved.  The  dust 
was  laid  along  the  floor  of  the  tube  and  along  the  shelves. 
A  small  gun  fired  at  some  point  in  the  tube  raised  a  cloud 
of  this  dust  just  as  the  gas  explosion  in  the  real  mine  would 
do.  Then  another  gun  was  fired  to  explode  the  dust-cloud. 
So  far  all  is  quite  simple  and  easy.  But  to  do  that  would 
be  of  no  value  without  the  means  of  finding  out  exactly  what 
resulted  from  the  explosion.  And  that  is  the  function  of 
the  instruments. 

To  commence  with,  there  is  the  great  wave  or  tide  of  force 
or  pressure  which  surges  along  the  gallery  immediately  the 
cloud  bursts  into  flame.  How  fast  does  that  wave  travel  ? 
How  long  is  it  after  the  explosion  before  the  shattering  effects 
of  it  are  felt  a  hundred  yards  away  ?  To  solve  that  problem 
electrical  contact-breakers  are  fixed  at  intervals  of  fifty  yards 
along  the  gallery.  Each  of  these  consists  of  a  cylinder  with 
a  piston  inside  it  something  like,  shall  we  say,  a  cycle  pump. 


AN  ARTIFICIAL  COAL  MINE  141 

The  piston,  held  down  normally  by  a  spring,  is  blown  up- 
wards by  the  force  of  the  explosion.  The  spring  is  adjustable, 
and  so  it  can  be  arranged  that  the  feeble  force  of  the  gun 
cannot  lift  the  piston,  but  the  more  powerful  coal-dust 
explosion  which  follows  can. 

Thus  when  the  explosion  takes  place  these  contact-breakers 
are  operated  in  succession.  The  one  nearest  the  seat  of  the 
disturbance  is  operated  first ;  next  the  one  fifty  yards 
farther  away  ;  then  the  one  a  hundred  yards  away,  and  so  on. 
The  moments  when  they  work  will  tell  the  speed  at  which 
the  blast  travels  along  the  gallery.  But  jt  travels  with  great 
speed,  and  so  to  measure  and  record  the  exact  moment  when 
each  contact-breaker  is  moved  is  a  matter  of  no  little 
difficulty.  Electricity,  however,  makes  this,  like  so  many 
other  things,  comparatively  easy. 

There  is  an  apparatus  used  in  astronomical  observatories 
called  a  chronograph,  which  registers,  within  a  small  fraction 
of  a  second,  the  moment  when  a  star  seems  to  pass  across 
a  wire  in  the  "  transit  circle,"  the  telescope  by  which  the 
positions  of  stars  are  determined  and  the  exact  time  kept. 
The  observer  sits  with  his  eye  to  the  telescope,  watching  the 
apparent  movement  of  the  star.  In  his  hand  he  holds  a 
small  "  push,"  pressure  on  which  by  his  fingers  operates  a 
minute  pricker,  which  acts  upon  a  moving  strip  of  paper. 
The  paper  travels  along  with  the  utmost  steadiness  and 
regularity,  while  a  clock  drives  a  sharply  pointed  pricker 
on  to  it  every  two  seconds.  Thus  the  clock  marks  out  the 
paper  into  lengths,  each  of  which  represents  two  seconds. 
But  the  other  pricker,  worked  electrically  by  the  observer's 
hand,  also  makes  its  mark  upon  the  paper,  and  so,  while 
the  regular  marks  indicate  intervals  of  two  seconds,  each 
irregular  one  marks  the  time  of  a  transit  or  passing  of  a  star 
across  the  wire.  An  examination  of  the  strip  subsequently 
enables  the  times  of  a  transit  to  be  seen  with  great  accuracy, 
from  the  position  of  the  corresponding  mark  between  two 
of  the  regular  marks. 

And  the  same  principle  was  applied  to  the  circuit-breakers 


142  AN  ARTIFICIAL  COAL  MINE 

of  this  artificial  mine.  Normally,  current  flows  through  the 
circuit-breaker,  but  the  lifting  of  the  piston  breaks  the 
circuit  (whence  the  name  of  the  contrivance),  and  that 
breaking  of  the  circuit  and  consequent  cessation  of  the 
current  operates  the  chronograph.  By  a  cleverly  con- 
structed device,  the  details  of  which  are  too  complicated  to 
set  out  here,  each  circuit-breaker  in  turn  makes  its  mark 
on  the  same  strip,  so  that  the  distances  apart  of  these  marks 
show  the  time  taken  by  the  force  of  the  explosion  to  travel 
fifty  yards.  Meanwhile  the  clock  goes  on  making  its  regular 
marks  (in  this  case  every  half-second),  so  that  they  form  a 
scale  by  which  the  other  intervals  can  be  measured  very 
exactly. 

The  chronograph  used  here  is  more  accurate  than  that  in 
use  at  Greenwich  Observatory,  the  reason  being  that  in  this 
case  the  recording  currents  are  sent  mechanically  by  the 
contact-breakers  operated  by  the  explosion  itself,  while  in 
the  case  of  the  astronomer  the  human  element  comes  in. 
To  watch  a  moving  speck  of  light  and  to  tell  exactly  when 
it  crosses  a  fine  line  is  by  no  means  easy,  and  so  to  tell  the 
time  within  a  tenth  of  a  second,  is  about  the  limit  of  possible 
accuracy.  The  instrument  we  have  been  referring  to, 
however,  can  register  the  time  which  a  gaseous  wave  moving 
3000  feet  per  second  takes  to  travel  fifty  feet.  In  other 
words,  the  circuit-breakers  can  be  operated  so  fast  that  when 
only  a  sixtieth  of  a  second  intervenes  between  the  action  of 
one  and  that  of  the  next  the  chronograph  can  duly  record 
the  fact. 

The  records  of  the  chronograph  can  be  made  in  two  ways : 
one  by  a  pen  on  a  piece  of  paper  tape,  and  the  other  by  a 
scratch  on  a  piece  of  smoked  paper. 

So  by  that  means  the  progress  of  the  "  force  "  of  the 
explosion  can  be  measured.  It  is  necessary  also  to  time  the 
movement  of  the  "  heat "  of  the  explosion,  for  the  two  may 
not  travel  together,  and  the  difference  between  them  may 
let  in  some  light  as  to  the  nature  and  behaviour  of  the 
explosion.  So  for  this  second  purpose  a  second  set  of 


AN  ARTIFICIAL  COAL  MINE  148 

circuit-breakers  are  used.  Each  of  these  consists  of  a  strip 
of  thin  tinfoil  stretched  across  the  gallery.  Being  placed 
edgeways  to  the  moving  current  of  gas,  the  force  of  the 
explosion  has  no  effect  upon  it,  but  the  heat  instantly  melts 
it.  Normally,  current  flows  through  the  strip,  and  so  the 
melting  is  signalised  by  the  cessation  of  the  current,  which 
event  is  recorded  by  the  chronograph. 

Thus  the  speeds  at  which  the  force  and  the  heat  of  the 
explosion  travel  are  ascertained.  Another  important  fact 
which  needs  to  be  found  is  the  amount  of  the  force,  or  the 
pressure,  at  different  points.  For  this  purpose  pressure- 
gauges  can  be  connected  to  the  gallery  at  the  desired  spots 
by  means  of  flexible  tubes.  This  flexible  tube  is  necessary 
in  order  that  the  vibration  of  the  steel  shell,  due  to  the 
explosion,  shall  not  be  communicated  to  the  instrument. 
The  pressure,  finding  its  way  along  the  flexible  pipe,  raises  a 
piston  against  the  force  of  a  spring,  and  the  distance  to  which 
it  is  raised  forms,  of  course,  a  measure  of  the  pressure  inside 
the  gallery  at  the  point  to  which  the  tube  is  connected. 
The  pressure  is  recorded  by  the  action  of  the  piston  in  moving 
a  style  which  just  touches  against  the  surface  of  a  moving 
paper.  There  are  three  styles  in  all  marking  this  paper. 
The  first  is  the  one  just  mentioned.  The  second  is  held  down 
on  to  the  paper  by  an  electro-magnet  energised  by  current 
flowing  through  a  line  wire  stretched  across  the  gallery  just 
where  the  explosion  originates.  This  line  wire  is  broken  at 
the  moment  of  the  explosion,  whereby  the  current  is  cut  off 
and  the  style  raised.  It  therefore  makes  its  mark  until  the 
moment  the  explosion  occurs,  and  then  leaves  off.  The  end 
of  that  line,  therefore,  shows  the  time  of  the  explosion. 
Meanwhile  the  first  style  is  drawing  a  straight  line,  but  as 
soon  as  the  pressure  begins  to  be  felt  by  the  pressure  recorder 
this  style  moves  and  the  line  slopes  upward.  Upward  it 
goes  as  the  pressure  increases,  until  it  has  reached  its  height, 
after  which  it  descends,  until  the  style  is  drawing  a  straight 
line  once  more.  Thus  the  rise  and  fall  of  the  line  represents 
the  rise  and  fall  of  the  force  of  the  explosion. 


144  AN  ARTIFICIAL  COAL  MINE 

Then  comes  the  matter  of  time.  How  soon  after  the 
explosion  occurred  did  the  pressure  begin  to  be  felt  ?  How 
long  did  it  take  to  reach  its  maximum  and  how  long  to  die 
out  again  ?  These  questions  need  answers  which  the  ap- 
paratus so  far  described  does  not  give.  True,  the  speed 
of  the  paper  may  be  known  approximately,  but  all  that  I 
have  described  will  occur  within  the  space  of  a  fraction  of  a 
second,  and  it  is  difficult  to  tell  the  speed  of  the  paper  with 
sufficient  accuracy.  Therein  we  see  the  purpose  of  the  third 
style.  It  is  attached  electrically  to  the  "  tenth-of-a-second 
time-marker."  This  consists  of  a  weight  suspended  at  a 
height.  The  force  of  the  explosion  lets  it  drop.  The  moment 
it  starts  to  fall  it  causes  the  style  to  make  a  mark  on  the 
paper.  When  it  has  fallen  a  certain  distance  the  style  makes 
another  mark.  And  the  distance  that  the  weight  falls 
between  the  making  of  the  two  marks  is  so  adjusted  that  the 
space  between  them  on  the  chart  represents  exactly  a  tenth 
of  a  second.  Thus  a  scale  is  formed  upon  the  chart  by  which 
the  other  times  can  be  measured.  There  is  the  line  terminat- 
ing at  the  moment  of  explosion  ;  the  straight  line  changing 
into  an  up-and-down  curve,  representing  the  time  and  the 
variation  of  the  pressure  ;  finally  there  are  the  two  marks 
representing  a  tenth  of  a  second  by  which  the  other  marks 
recorded  upon  the  chart  can  be  interpreted. 

But  the  mere  pressure  and  velocity  of  the  explosion  form 
but  a  part  of  the  knowledge  desired.  How  the  explosion  is 
formed,  whether  or  not  the  coal-dust  is  burnt  up  entirely, 
whether,  indeed,  it  be  the  dust  itself  which  burns  or  coal-gas 
given  off  by  the  dust  under  the  heat  of  the  preliminary 
explosion,  wrhat  the  gas  is  which  is  left  by  the  explosion  at 
various  stages — these  are  important  things  to  be  known, 
and  they  can  only  be  ascertained  by  taking  samples  of  the 
gases  in  the  gallery  at  different  moments  during  and  after 
the  explosion.  To  obtain  these  samples  bottles  are  used, 
but  the  question  is  how  to  get  them  filled  at  just  the  right 
time.  Into  the  shell  of  the  gallery  holes  are  drilled,  and  to 
these  the  metal  bottles  or  flasks  are  screwed,  a  pipe  leading 


AN  ARTIFICIAL  COAL  MINE  145 

from  the  mouth  of  each  bottle  well  in  towards  the  centre  of 
the  gallery.  The  end  of  this  tube  is  closed  by  a  cap  of  glass 
above  which  there  stands  poised  a  little  hammer.  Con- 
trolling the  hammer  is  an  electrical  device  called  a  "  contact- 
maker,"  so  arranged  that  just  at  the  desired  moment  the 
hammer  falls,  breaking  the  glass,  and  admitting  a  sample  of 
the  gas  in  the  gallery,  the  bottle  and  its  tube  having  previously 
had  the  air  exhausted  from  them,  so  that  on  the  glass  being 
broken  the  gas  is  sucked  in. 

At  the  same  moment  a  weight  falls,  attached  to  the  end 
of  a  cord,  and  this,  on  reaching  the  end  of  its  tether,  closes 
the  end  of  the  tube,  and  the  sample  is  imprisoned  until  such 
time  as  the  bottle  can  be  disconnected  and  taken  away  to  the 
laboratory  for  its  contents  to  be  analysed. 

The  contact-makers  are  of  two  kinds.  In  one  the  pressure 
of  the  explosion  raises  a  piston  which  completes  a  circuit 
allowing  current  to  flow  through  the  very  fine  wire  which 
prevents  the  fall  of  the  hammer.  This  fine  wire  being  fused 
by  the  current,  the  hammer  falls  and  does  its  work.  The 
other  kind,  which  are  used  when  the  force  of  the  explosion 
is  not  enough  to  raise  a  piston,  is  operated  by  one  of  the  tin- 
foil circuit-breakers.  A  magnet,  being  energised  by  current 
passing  through  the  foil,  holds  up  a  curved  bar  over  two  cups 
of  mercury.  Broken  by  the  heat  of  the  explosion,  the  foil 
cuts  off  this  current,  de-energises  the  magnet,  and  allows 
the  bar  to  fall  with  its  ends  in  the  mercury.  This  completes 
another  circuit,  permitting  current  to  pass  to  the  fine  wire, 
whereby  the  hammer  is  released.  By  connecting  a  bottle 
to  a  contact-maker  at  a  distance  the  sample  can  be  obtained 
at  any  desired  period  of  the  explosion.  If,  for  instance,  the 
sample  is  to  represent  the  immediate  products  of  combustion, 
it  is  placed  near  to  the  contact-maker.  Then  the  sample  is 
drawn  in  practically  at  the  moment  of  explosion.  If,  on 
the  other  hand,  it  is  the  after-damp  that  is  to  be  sampled, 
then  the  bottle  would  be  connected  to  a  contact-maker  a 
long  way  from  the  seat  of  the  explosion,  with  the  result  that 
its  glass  cap  would  not  be  broken  until  some  considerable 
K 


146  AN  ARTIFICIAL  COAL  MINE 

time  had  elapsed  after  the  explosion  has  passed  the  bottle. 
The  time  also  during  which  the  bottle  is  drawing  in  its 
sample  can  be  adjusted  by  varying  the  length  of  the  cord  to 
which  the  weight  is  attached. 

And  last  of  all  must  be  mentioned  the  employment  of  a 
kinematograph,  capable  of  taking  twenty-two  photographs 
per  second,  for  observing  the  effects  at  the  ends  of  the 
gallery  (see  illustrations). 

Thus  records  are  obtained  of  the  force  and  heat  of  the 
explosion,  its  mechanical  and  thermal  effects  upon  the  walls 
of  the  gallery,  or,  if  it  were  in  a  real  pit,  the  effects  which  it 
would  have  in  shaking  and  in  heating  the  workings,  and  the 
men  labouring  in  them.  This  and  the  analysis  of  the  gases 
producing  and  produced  by  the  explosion,  derived  from  the 
contents  of  the  bottles,  give  sound  data  upon  which  can  be 
built  up  reliable  theories  as  to  the  nature  of  colliery  explosions 
and  the  way  to  prevent  them,  results  which  could  be  obtained 
in  no  other  way.  No  one  can  help  being  struck  with  the 
thoroughness  and  ingenuity  of  the  means  adopted  to  these 
ends,  and  it  is  no  exaggeration  to  say  that  it  is  a  splendid 
example  of  thoroughly  scientific  methods  applied  to  an 
important  industrial  investigation.  It  will  be  interesting 
to  conclude  this  account  with  a  brief  mention  of  some  of 
the  results  to  which  these  painstaking  efforts  have  led. 

First  in  importance  the  fact  is  placed  beyond  doubt  that 
coal-dust,  which  in  bulk  will  only  burn  slowly,  will,  when 
well  mixed  with  air,  explode.  And  no  combustible  gas 
need  be  present  to  aid  in  the  explosion. 

The  dust-raising  gun,  by  blowing  some  dust  into  a  cloud 
which  was  ignited  by  the  second  gun,  caused  an  explosion 
powerful  enough  to  do  all  the  damage  experienced  in  the 
most  disastrous  natural  explosions.  So  it  is  practically 
certain  that  the  function  of  the  gas  is  but  that  of  the  first 
gun,  to  raise  the  cloud  of  dust. 

A  typical  experimental  explosion  may  be  briefly  described. 
On  the  cloud-raising  gun  being  fired  a  small  cloud  of  dust 
was  driven  out  of  the  ends  of  the  gallery,  even  that  end  at 


AN  ARTIFICIAL  COAL  MINE  147 

which  the  fan  was  blowing  air  in.  In  other  words,  the 
current  of  air  was  checked,  even  reversed,  by  the  pre- 
liminary shock.  This  cloud  was,  of  course,  shown  by  the 
kinematograph. 

Then  when  the  second  gun  was  fired,  and  the  real  coal- 
dust  explosion  occurred,  there  was  first  a  cloud  of  dust  shot 
out  larger  than  the  other  one,  to  be  followed  by  a  cloud  of 
flame  180  feet  long.  These  also  were  recorded  by  the  kine- 
matograph. The  sound  was  heard  seven  miles  away. 

Pressures  as  high  as  92  Ib.  per  square  inch  were  recorded, 
and  the  force  of  the  blast  was  found  to  travel  well  over 
2000  feet  per  second. 

In  many  cases,  strange  to  say,  the  effects  were  very  slight 
at  the  seat  of  the  disturbance,  the  force  seeming  to  increase  as 
the  wave  travelled  along  the  gallery.  Probably  the  dust  had 
not  time  to  burn  completely  but  only  partially  at  the  first 
onset.  Where  props  or  timbers  checked  the  flow  of  the 
flaming  gases  there  the  damage  was  most,  for  no  doubt  the 
eddies  caused  the  air  and  coal  to  be  particularly  well  mixed 
at  such  points.  An  encrustation  of  coke  was  found  on  the 
sides  and  the  timbers  after  all  was  over,  probably  because 
there  was  not  sufficient  air  to  burn  all  the  dust,  and  some 
was  only  heated  into  coke  to  be  deposited  on  the  nearest 
surface,  where  the  tarry  matters  would  make  it  stick. 

Finally,  the  most  important,  perhaps,  of  all,  it  was  demon- 
strated that  an  admixture  of  stone-dust  with  the  coal-dust 
made  it  non-inflammable.  If  a  small  zone  were  treated  in  this 
way,  stone-dust  being  mingled  with  the  other,  the  explosion 
became  stifled  at  that  point.  True,  the  poisonous  after- 
damp swept  on  beyond,  so  that  men  there  might  have  been 
poisoned  by  it,  but  the  stone  zone  would  certainly  save  them 
from  the  direct  effects  of  the  blast.  If,  however,  stone-dust 
be  mingled  with  coal-dust  all  along  the  gallery,  then  no 
explosion  at  all  would  occur,  again  proving  that  it  is  the 
coal-dust  which  does  the  damage. 

In  the  colliery  adjoining  the  experimental  gallery  this  plan 
had  been  in  use  for  years.  Soft  shale  is  ground  to  fine 


148  AN  ARTIFICIAL  COAL  MINE 

powder,  and  is  sprinkled  wherever  coal-dust  has  collected. 
It  is  just  strewn  by  hand,  giving  the  workings  the  appear- 
ance of  having  been  roughly  whitewashed.  And  since  that 
has  been  done  there  has  been  no  explosion  in  that  pit. 
The  experiments  showed  beyond  doubt  that  that  was  no 
chance  occurrence.  They  showed  that  in  some  way  not 
thoroughly  understood  this  addition  of  stone-dust  renders 
the  coal-dust  harmless.  It  may  be  that  it  merely  dilutes  it. 
It  may  be  that  in  some  way  it  takes  some  of  the  heat  and 
so  prevents  the  coal  particles  becoming  hot  enough.  It  may 
be  that,  being  a  little  heavier,  it  checks  the  formation  of  the 
dust-cloud.  However  that  may  be,  there  is  no  doubt  now 
that  stone-dust  is  the  salvation  of  the  miner  so  far  as 
explosions  are  concerned. 

Water  sprinkled  upon  the  coal-dust,  by  laying  it  and 
keeping  it  from  forming  a  cloud,  has  the  same  effect,  but  it  is 
less  convenient,  for  the  simple  reason  that  water  evaporates, 
while  stone-dust  stays  where  it  is  put. 


CHAPTER  XII 

THE  MOST  STRIKING  INVENTION   OF  RECENT  TIMES 

PROBABLY  no  invention  has  made  such  a  sensation 
during  recent  years  as  wireless  telegraphy.    And 
since  it  is  the  direct  outcome  of  the  most  abstruse, 
purely  scientific   investigations,  there   could  be  no  more 
appropriate  subject  for  a  place  in  this  book. 

For  many  years  there  has  been  a  belief  in  the  existence  of 
a  mysterious  something  to  which  has  been  given  the  name 
of  "The  Ether."  Totally  different,  it  should  be  noted, 
from  the  chemical  of  the  same  name,  it  is  entirely  a  creature 
of  the  intellect.  None  of  our  senses  give  us  the  slightest 
direct  indication  of  its  existence.  No  one  has  either  seen, 
felt,  heard,  smelt  or  tasted  it.  Yet  we  feel  that  it  must 
exist,  for  the  simple  reason  that  some  things  which  our 
senses  do  tell  us  of  are  utterly  inexplicable  without  it. 

It  was  originally  thought  of  in  connection  with  light. 
Standing  at  night  upon  the  top  of  a  hill,  we  see  the  lights 
of  a  town  a  mile  away.  How  is  it  that  those  distant  gas  or 
electric  lamps  affect  our  eyes  ?  They  are  a  mile  away ; 
and  the  idea  that  one  object  can  affect  another  at  a  distance 
is  one  which  the  human  mind  refuses  to  accept.  We  feel 
compelled  to  believe  that  there  is  something  in  contact  with 
the  source  of  light  which  is  affected  first,  and  through  which 
the  disturbance,  whatever  it  may  be,  is  conveyed  to  our 
eyes,  with  which  it  must  also  be  in  contact.  We  feel  that 
there  must  be  a  something  stretching  from  our  eyes  to  the 
distant  objects,  by  which  the  light  is  carried.  Of  course 
the  air  fills  the  space  referred  to,  but  that  cannot  be  the 
carrier  of  light,  for  if  we  look  through  a  glass  vessel  from 
which  the  air  has  been  exhausted  we  see  distant  objects 
149 


150  THE  MOST  STRIKING  INVENTION 

undimmed.  We  also  have  good  reason  to  believe  that  the 
air  belongs  specially  to  our  globe,  and  does  not  extend 
upwards  for  more  than  a  few  miles.  Consequently  it  cannot 
be  air  which  brings  sunlight  and  starlight.  We  are  forced 
to  fall  back,  therefore,  upon  the  belief  in  something,  of  which 
we  have  no  other  knowledge,  which  must  fill  all  the  vacant 
spaces  in  the  whole  universe,  passing,  even,  between  the 
particles  of  which  ordinary  matter  is  composed,  reaching  as 
far  as  the  remotest  star,  able  to  penetrate  everything,  and 
consequently  not  excludable  from  the  most  perfect  vacuum. 
It  is  something  so  different  from  anything  of  which  we  have 
any  direct  knowledge  that  one  is  tempted  sometimes  to 
doubt  whether  there^must  not  be  some  other  explanation  of 
light.  In  order  to  transmit  light  at  the  speed  at  which  we 
find  that  it  does  in  fact  travel,  the  ether  must  be  more  rigid 
than  the  hardest  substance  we  know  of.  Many,  many 
thousand  times  more  rigid,  indeed.  Yet  it  seems  to  offer 
no  resistance  to  the  passage  of  the  planets  through  it. 
Still,  there  is  no  other  alternative,  so  far  as  men  can  conceive, 
and  we  are  compelled,  therefore,  to  believe  in  the  existence 
of  the  ether. 

The  first  things  discovered  by  the  telescope  were  the 
larger  satellites  of  Jupiter.  With  that  precision  for  which 
astronomers  are  noted,  they  soon  drew  up  time-tables, 
showing  not  only  the  past  movements  of  these  bodies,  but 
also  their  future  ones.  They  were  soon  puzzled,  however, 
by  the  obvious  fact  that  the  moons  of  Jupiter  were  not 
working  according  to  schedule,  to  use  a  railway  expression. 
They  got  later  and  later  for  a  time,  and  then  gradually 
quickened  up  until  they  got  too  fast.  Then  they  slowed 
down  again.  This  repeated  itself,  and  is  going  on  still, 
with  this  difference,  however,  that  the  cause  has  been 
discovered  and  the  schedules  amended  accordingly.  The 
solution  of  the  puzzle  was  that  when  the  earth  and  the  great 
planet  are  on  the  same  side  of  the  sun  they  are  some  186 
millions  of  miles  nearer  together  than  when  they  are  on 
opposite  sides  of  the  sun.  The  evolutions  of  the  satellites 


OF  MODERN  TIMES  151 

are  quite  regular,  according  to  the  astronomers'  calculations, 
but  they  seemed  to  the  earthly  astronomers  to  vary,  because 
of  the  time  which  light  took  to  traverse  that  186  millions 
of  miles.  When  the  two  bodies  were  nearest  together 
the  occurrences  seemed  to  happen  about  1000  seconds 
(16  minutes)  earlier  than  when  they  were  farthest  apart. 
Consequently  it  became  evident  that  light  took  1000 
seconds  to  travel  186  million  miles,  or  that,  in  other  words, 
it  moved  at  the  prodigious  speed  of  186  thousand  miles  per 
second.  That  discovery  was,  of  course,  many  years  ago, 
but  experiments  since  have  proved  the  figure  mentioned  to 
be  about  right. 

It  put  beyond  question  the  fact  that  the  action  of  a  distant 
light  upon  the  eye  was  not  an  "  action  at  a  distance,"  for 
such  action,  were  it  possible,  would  take  effect  at  once. 
Seeing  that  light  passed  from  the  distant  satellites  at  a 
definite  velocity,  and  took  a  certain  time  to  reach  us,  it  was 
evident  that  it  was,  during  that  time,  passing  through  a 
medium  of  some  sort,  and  that  medium  must  be  the  ether, 
for  no  alternative  explanation  will  suffice. 

So  it  became  recognised  that  light  really  consists  of  waves 
or  undulations  of  some  sort  in  the  ether ;  that  a  distant, 
luminous  body  set  these  waves  going  ;  that  they  travelled 
with  a  definite  velocity,  and  then,  striking  our  eyes,  produced 
the  sensation  known  as  light.  Many  things  were  found  out 
about  light  in  the  years  which  followed  the  discovery  of  its 
velocity.  The  lengths  of  the  waves  were  ascertained — that 
is  to  say,  the  distance  from  the  crest  of  one  to  the  crest  of 
the  next.  The  different  lengths  were  sorted  out  and  found 
to  give  rise  to  different  colours,  while  longer  waves,  which 
produced  no  sensation  of  light,  were  found  to  carry  heat, 
thereby  explaining  how  the  heat  reaches  us  from  a  distant 
fire,  or  from  the  sun. 

Of  the  actual  nature  of  the  waves,  however,  little  was 
known,  although  there  was  a  vague  idea  that  they  were 
connected  in  some  way  with  electricity,  at  which  point  in  the 
story  there  comes  in  the  famous  name  of  James  Clerk 


152  THE  MOST  STRIKING  INVENTION 

Maxwell,  a  professor  of  Cambridge  University,  who  in  1864 
produced  before  the  Royal  Society  the  explanation  of  the 
nature  of  the  waves  and  their  connection  with  electricity 
and  magnetism.  That  in  itself  was  a  wonderful  achieve- 
ment, but  far  more  wonderful  still  is  the  fact  that  he  truly 
predicted  the  existence  of  longer  waves  than  any  then 
known,  which  no  one  knew  how  to  cause,  or  how  to  detect 
if  caused.  That  prediction  has  since  been  fulfilled.  The 
long  waves  have  been  found ;  we  know  how  to  make  them 
and  how  to  perceive  their  presence.  They  are  the  messengers 
which  carry  our  wireless  messages. 

The  discovery  of  these,  at  that  time  unknown  waves,  on 
paper,  by  simply  calculating  and  reasoning  about  them, 
is  more  marvellous  even  than  the  feat  of  Adams  and  Le 
Verrier  in  discovering  a  planet  on  paper  before  anyone  had 
seen  it.  It  established  Maxwell  among  the  heroes  of  science 
for  all  time. 

A  magnet  acts  upon  a  piece  of  iron  some  distance  away. 
The  pull  must  be  transmitted  through  some  kind  of  ether. 
A  current  of  electricity  behaves  in  the  same  way,  acting 
precisely  as  a  magnet,  with  power  to  affect  things  at  a 
distance.  Again  an  ether  is  necessary.  A  dynamo  works 
by  moving  a  magnet  past  a  wire  which  it  does  not  touch, 
thereby  generating  current  in  it.  There  again  an  ether 
is  necessary  to  transmit  the  effect  from  the  one  to  the 
other. 

Taking,  then,  the  known  magnetic  effects  of  an  electric 
current  and  the  electrifying  effects  of  magnets,  he  was  able 
to  show  that  the  same  ether  accounted  for  all,  and  for  the 
transmission  of  light  as  well,  that,  in  fact,  there  was  but  one 
ether  which  performed  all  these  various  duties. 

He  proved  from  the  known  facts  about  electricity  and 
magnetism  that  waves  such  as  he  imagined  would,  in  fact, 
move  with  the  speed  of  light.  And  once  knowing  the  nature 
of  the  waves,  he  asserted  that  in  all  probability  there  were 
others  of  which  men  had  then  no  practical  knowledge. 
Maxwell's  theory  soon  set  experimenters  searching  for  the 


OF  MODERN  TIMES  158 

means  of  producing  the  long  waves  which  he  had  predicted 
would  be  found. 

Several  authorities  had  before  then  stated  their  belief 
that  the  current  derived  from  a  Leyden  jar  was  not  simply 
a  flow  in  one  direction.  They  suggested,  and  gave  grounds 
for  the  belief,  that  the  current  surged  to  and  fro  for  some 
time  before  it  settled  down  ;  that  it  swung  to  and  fro,  indeed, 
like  a  pendulum. 

There  may  be  some  of  my  readers  who  are  unacquainted 
with  this  interesting  piece  of  electrical  apparatus  the  Leyden 
jar.  It  is  a  convenient  form  of  what  is  called  an  electro- 
static condenser.  This  is  two  conductors,  generally  in  the 
form  of  two  plates  with  an  insulator  between  them.  In  the 
Leyden  jar  the  insulator  is  a  glass  jar,  while  the  "  plates  " 
are  coatings  of  tinfoil,  one  inside  and  the  other  outside.  On 
connecting  one  coating  to  one  pole  of  a  battery,  and  the  other 
to  the  other  pole,  they  become  charged,  one  positively  and 
the  other  negatively.  One,  that  is,  acquires  an  excess  of 
electricity,  while  the  other  becomes  deficient  to  an  exactly 
similar  extent.  When  the  two  are  afterwards  connected  by 
a  wire  the  surplus  on  one  flashes  through  it  to  make  good 
the  deficiency  on  the  other. 

Rushing  first  of  all  from  positive  coating  to  negative, 
electrical  inertia  causes  it  to  overshoot  the  mark  and  to 
recharge  the  jar  with  the  charges  reversed.  Then  current 
begins  to  flow  back  again,  doing  the  same  several  times 
over,  until  at  last  equilibrium  is  established. 

The  power  to  absorb  and  hold  a  charge  of  electricity, 
which  is  the  characteristic  of  a  condenser,  is  called  "  capacity." 

What,  then,  is  "  electrical  inertia "  ?  I  have  already 
referred  to  the  effect  which  the  creation  of  a  magnetic  field 
around  a  current  has  upon  neighbouring  conductors.  It  also 
has  an  effect  upon  itself.  As  soon  as  the  current  begins 
to  flow  it  builds  up  the  magnetic  field,  and  in  the  process 
some  of  its  energy  is  exhausted.  On  the  original  current 
ceasing,  however,  the  magnetic  field  collapses  back  on  to 
the  conductor  once  more  and  in  so  doing  restores  that 


154  THE  MOST  STRIKING  INVENTION 

energy.  This  occurs  whenever  current  flows,  but  it  is 
specially  noticeable  in  long  conductors,  like  submarine  cables. 
In  them  the  battery  has  to  act  for  a  considerable  time  before 
any  current  reaches  the  farther  end.  It  is  in  the  meantime 
employed  in  building  up  the  magnetic  field  around  the  wire. 
Then  when  the  battery  has  ceased  to  act  the  current  still 
comes  flowing  out  at  the  farther  end — the  magnetic  field  is 
giving  back  the  energy  expended  upon  it.  Thus  a  current 
is  reluctant  to  start  flowing  through  a  conductor,  and,  having 
started,  is  disinclined  to  stop.  This  is  called  "  inductance," 
and  it  has  exactly  the  same  effect  upon  the  current  that 
inertia  has  upon  a  body.  What  inertia  is  to  a  material 
body  inductance  is  to  an  electric  current. 

And  lastly,  the  resistance  which  the  conductor  offers  to 
the  passage  of  the  current  is  precisely  analagous  to  the 
friction  of  the  water  in  a  pipe. 

So,  we  see,  the  "  capacity  "  of  the  two  coatings  of  the  jar 
and  the  inductance  which  occurs  in  the  connecting  wire 
cause  the  current  to  oscillate  to  and  fro  for  a  while  when  the 
jar  is  discharged,  which  surging  or  oscillation  is  ultimately 
stopped  by  the  resistance  of  the  wire.  The  two  coatings 
and  the  wire  form  what  is  called  an  oscillatory  circuit. 

We  can  now  resume  our  story. 

After  much  experimenting  Hertz,  of  Carlsruhe,  discovered 
the  fact  that  when  a  discharge  was  taking  place  in  an 
oscillatory  circuit  tiny  sparks  passed  between  the  ends  of  a 
curved  wire  held  some  distance  away.  His  apparatus  is 
illustrated  in  Figs.  6  and  7.  The  former,  which  is  termed 
nowadays  a  "  Hertz  Oscillator,"  is  simply  two  metal  discs 
almost  connected  by  a  thick  wire.  The  wire  is  broken, 
however,  at  the  centre,  and  the  two  halves  terminate  in 
two  metal  balls.  Each  ball  is  connected  to  one  terminal 
of  an  induction  coil.  Now  the  current  comes  from  an 
induction  coil  in  a  series  of  spurts.  It  is  not  an  alternating 
current  exactly  (since  every  alternate  current  is  so  feeble 
as  to  be  negligible),  but  is  practically  an  intermittent  current 
always  in  the  same  direction.  Thus  we  may  call  one  the 


OF  MODERN  TIMES 


155 


positive  end  of  the  coil  and  the  other  the  negative,  A  short 
current  comes  along  with  every  backward  movement  of  the 
little  vibrating  arm  which  forms  a  part  of  the  apparatus. 
This  breaking  of  the  "  primary  "  circuit  may  take  place 
perhaps  fifty  times  per  second,  so  that  the  intermittent 
"  secondary  "  currents  will  succeed  each  other  at  intervals 
of  a  fiftieth  of  a  second,  or  even  less.  The  brain  reels  at  the 
attempt  to  think  of  a  fiftieth  of  a  second,  but  it  is  really 
quite  a  long  interval  as  these  things  go,  and  during  that 


FIG.  6.— The  apparatus  by  which  Hertz  made  his  discoveries,  hence 
called  the  Hertz  Oscillator,  a  a  are  metal  plates ;  d  is  the  spark-gap 
between  the  two  metal  balls ;  6  is  the  battery,  and  c  the  induction  coil. 

interval  quite  a  lot  happens.  For  the  current  first  of  all 
charges  the  two  plates  as  a  condenser. 

When  they  are  as  full  as  they  will  hold  the  current  over- 
flows, as  it  were,  across  the  gap  between  the  two  balls. 

Now  an  air-gap — a  gap  that  is  filled  with  air,  between  two 
conductors — is  a  very  strong  insulator.  But  when  current 
has  once  broken  through  it  it  becomes  a  fairly  good  con- 
ductor. Hence  as  soon  as  the  first  spark  has  passed  between 
the  two  knobs  the  plates  become  connected  almost  as  if  a 
wire  were  passed  from  one  to  the  other.  And  there  we  have 
quite  a  good  oscillatory  circuit.  There  is  capacity  at  each 
end  and  a  fairly  long  length  of  wire  to  provide  the  inductance. 
Consequently  that  breakdown  of  the  insulation  of  the  air 


156          THE  MOST  STRIKING  INVENTION 

in  the  spark-gap  is  followed  by  electrical  oscillations  which 
take  place  with  inconceivable  rapidity.  Yet  because  of  the 
resistance  of  the  spark-gap,  which  is  considerable  even  after 
it  has  been  broken  through,  the  oscillations  do  not  continue 
for  long.  They  have  died  away  long  before  the  lapse  of  a 
fiftieth  of  a  second,  when  the  next  impulse  comes  along  from 
the  coil.  In  the  meantime  the  air-gap  regains  its  insulating 
properties,  and  so,  on  the  arrival  of  the  next  impulse,  the 
whole  thing  occurs  once  more. 

Thus  a  little  train  of  oscillations  is  produced  for  every 
impulse  from  the  coil.    Every  train  causes  a  corresponding 
disturbance  in  the  ether,  and  sends  off  a 
train  of  electro-magnetic  waves,  and  these, 
falling  upon  the  distant  wire,  generate  in 
it  a  train  similar  to  that  which  brought 
them  into  being.    These  trains,  in  Hertz' 
simple  apparatus,  manifested  themselves 
in   the   form    of   minute   sparks    leaping 
FIG.  7.  across  the  small  gap  between  the  ends  of 

Hertz "  Detector."  .  °.       ^ 

It  was  with  this  simple   the  CUFVCd  Wire    (Fig.  7). 
apparatus  that  Hertz  dis-          _  .  ^\    f,      ; '    __.  _        . .  . 

covered  how  to  detect  the  It  was  in  1888  that  Hertz  made  this 
discovery  of  a  way  to  detect  long  electric 
waves.  He  subjected  the  matter  to  many  more  experi- 
ments and  found  that  the  waves  have  many  points  in 
common  with  light  rays.  He  found  that  they  were  re- 
flected from  certain  surfaces,  just  as  light  is  reflected  from 
the  surface  of  a  mirror.  He  made  prisms  which  were 
able  to  bend  them  as  light  waves  are  bent  by  a  prism  of 
glass.  Some  things  appeared  to  be  transparent  to  them,  as 
clear  glass  is  to  light,  while  others  are  opaque.  It  does  not 
follow  that  the  same  things  which  reflect  light  waves  reflect 
electric  waves,  and  so  on.  The  latter  can  pass  through  a 
brick  wall,  for  example.  But  the  same  divergence  is  to  be 
observed  between  light  and  radiant  heat,  of  which  the  action 
of  glass  is  a  familiar  example.  Clear  glass  will  let  light 
through  almost  undimmed,  yet  we  use  it  for  fire-screens  to 
shield  us  from  too  much  radiant  heat.  The  important  fact 


OF  MODERN  TIMES  157 

is  that  all  three — light,  radiant  heat  and  Hertzian  waves — 
in  addition  to  travelling  at  the  same  speed,  are  reflected, 
absorbed  or  refracted,  according  to  precisely  the  same 
principles.  This  is  almost  perfect  testimony  to  their 
essential  identity. 

The  difference  between  them,  as  has  been  said  already,  is  the 
distance  from  crest  to  crest  of  the  waves — the  "wave-length," 
that  is.  And  the  reader  will  wonder  by  what  manner  of 
means  this  mysterious  dimension  can  be  ascertained.  In 
spite  of  its  seeming  mystery  the  method  is  very  simple. 

It  is  based  upon  the  fact  that  two  sets  of  similar  waves 
travelling  at  the  same  speed  in  opposite  directions  interfere 
with  one  another  in  a  peculiar  way.  Suppose  that  one  set 
of  waves  travel  along  to  a  reflector  and  strike  it  vertically  ; 
then  another  set  will  travel  back  from  the  reflector  exactly 
similar  to  the  first,  except  that  their  direction  will  be  opposite. 
And  the  result  will  be  that  at  certain  intervals  they  will 
exactly  neutralise  each  other,  so  that  at  those  points  there 
will  be  no  wave-action  appreciable  at  all.  Those  points 
where  no  action  is  to  be  perceived  are  called  "  nodes,"  and 
they  are  exactly  half  a  wave-length  apart. 

This  will  be  quite  easily  understood  from  the  accompany- 
ing diagrams.  In  each  of  these  diagrams  the  set  of  waves 
marked  a  are  supposed  to  be  moving  from  left  to  right, 
while  those  denoted  by  b  are  reflected  back  and  are  moving 
from  right  to  left.  It  will  be  noticed  that  each  wavy  line 
has  a  straight  line  drawn  through  it,  dividing  it  into  alter- 
nate crests  and  hollows,  which  line  is  known  as  the  axis  of 
the  waves. 

Now  notice  that  in  Fig.  8  there  are  points  marked  X, 
where  the  a  waves  are  just  as  much  above  the  axis  as  the 
b  waves  are  below  it,  and  vice  versa.  Hence  at  those  points 
the  two  sets  of  waves  will  neutralise  each  other. 

Now  turn  to  the  next  figure,  which,  be  it  remembered, 
shows  the  same  waves  a  moment Jater,  when  they  have  moved 
a  little  farther  on  in  their  respective  journeys,  and  it  will 
be  seen  that  there,  too,  are  places  marked  x  where  the  two 


158 


THE  MOST  STRIKING  INVENTION 


sets  of  waves  neutralise  each  other.  And  the  same  with  the 
third  diagram. 

And  finally  observe  that  the  places  marked  X  are  always 
the  same  in  all  the  diagrams  —  that  is  to  say,  they  are  always 
the  same  distance  from  the  line  on  the  right-hand  side,  which 
denotes  the  reflector.  It  will  be  clear,  too,  that  each  node 
is  half  a  wave-length  from  the  next. 

Thus  it  can  be  shown  that  at  every  moment,  and  not 
merely  at  the  three  indicated  in  the  diagrams,  the  two  sets 


FIGS.  8,  9  and  10.— These  diagrams  help  us  to  see  how  the  "wireless  waves"  are 
measured.  The  a  waves  are  supposed  to  be  moving  from  left  to  right  and  the  &  waves 
from  right  to  left.  At  the  points  marked  x  they  neutralise  each  other.  It  is  then 
easy  to  discover  those  points  and  the  distance  apart  of  any  two  adjacent  ones  is  half 
the  "wave-length." 

N.B.— In  Fig.  10  the  6  waves  fall  exactly  on  top  of  the  «  waves. 

neutralise  each  other  at  the  nodes,  that  the  nodes  are  always 
in  the  same  places  and  half  a  wave-length  apart. 

Everywhere  else,  except  at  the  nodes,  there  is  action 
more  or  less  energetic,  but  there  is  perpetual  calm. 

But  how  can  we  tell  where  the  nodes  are  ?  When  we 
recollect  that  they  are  points  at  which  no  wave-motion  at 
all  takes  place  it  is  easy  to  see  that  we  shall  at  those  points 
get  no  spark  in  our  detector.  So  what  Hertz  did  was  to  set 
his  oscillator  going  so  that  it  threw  waves  upon  a  reflecting 
surface  and  then  move  his  detector  to  and  fro  in  the  neigh- 
bourhood until  he  found  the  nodes.  Between  the  nodes, 


OF  MODERN  TIMES  159 

as  will  be  seen  by  an  inspection  of  the  curves  once  more, 
there  are  other  points  at  which  the  wave-action  will  be  twice 
as  great  as  with  the  single  wave,  and  so  at  those  points  the 
response  of  the  detector  would  be  especially  energetic. 

This  mutual  action  between  an  incident  wave  and  a 
reflected  wave  is  termed  "  interference,"  and  by  it  the  wave- 
lengths of  all  the  ethereal  waves  have  been  measured.  The 
plan  used  in  the  case  of  light  waves,  although  the  same  in 
principle,  is  somewhat  different  because  of  the  extreme 
shortness  of  the  waves. 

So  the  experiments  of  Hertz  not  only  showed  that  long 
electric  waves  existed,  but  that  they  were  in  all  essentials 
similar  to  light,  and  their  wave-lengths  were  ascertained. 
On  that  basis  has  been  built  up  modern  wireless  telegraphy. 

It  may  be  interesting  to  mention  at  this  point  a  very 
curious,  and  in  a  sense  pathetic,  incident.  Professor  Hughes, 
whose  name  is  associated  with  certain  well-known  instru- 
ments for  ordinary  telegraphy,  nine  years  before  Hertz' 
discovery  noticed  that  a  microphone  was  affected  by  the 
action  of  an  induction  coil  some  distance  away.  He  himself 
attached  some  importance  to  the  matter,  but  he  allowed 
himself  to  be  dissuaded  from  following  up  the  discovery  by 
other  scientists,  more  eminent  than  himself  at  the  time,  who 
thought  that  it  was  not  a  promising  field  for  investigation. 
But  for  the  influence  of  these  friends  he  would  possibly  be 
the  hero  of  this  story  in  place  of  Hertz. 

Professor  Silvanus  Thomson  has  said  that  he  too  noticed 
the  sparks  produced  at  a  distance  when  a  Leyden  jar  was 
discharged,  but  he  makes  no  claim  to  precedence  over  Hertz, 
since,  seeing  the  phenomenon,  he  did  not  perceive  its  real 
meaning,  while  Hertz,  though  a  little  later  in  time,  realised 
the  profound  significance  of  it. 

Hertz  himself  in  his  account  of  his  experiments  is  gener- 
ous enough  to  assert  that,  had  he  not  discovered  the  waves 
when  he  did,  he  is  quite  certain  that  Sir  Oliver  Lodge  would 
have  done  so. 

Before  proceeding  to  describe  the  principal  apparatus  used 


160  THE  MOST  STRIKING  INVENTION 

in  the  wireless  station  I  should  like  to  devote  a  little  space 
to  the  explanation  of  a  term  which  will  come  up  again  and 
again,  and  which  represents  that  which  is  responsible,  in 
the  main,  for  the  marvellous  advances  which  the  art  of 
sending  wireless  messages  has  achieved  in  the  last  few  years. 
I  refer  to  "  resonance." 

It  will  be  a  great  help  if  the  reader  will  try  for  himself 
a  simple,  inexpensive  little  experiment.  Stretch  a  string 
horizontally  across  a  room  and  on  to  it  tie  two  other  strings 
so  that  they  hang  down  vertically  a  little  distance  apart. 
To  the  ends  of  the  two  strings  tie  some  small  objects — a 
cotton  reel  on  each  will  answer  admirably.  They  will  thus 
form  two  pendulums,  and,  to  commence  with,  they  should  be 
just  the  same  length.  Having  rigged  all  this  up,  give  one 
pendulum  a  good  swing.  It  will  impart  motion  of  a  to-and- 
fro  variety  to  the  supporting  string,  which  in  its  turn  will 
pass  that  motion  on  to  the  other  pendulum.  In  a  very  short 
time,  then,  the  second  pendulum  will  be  vibrating  like  the 
first.  Indeed  the  whole  motion  of  the  first  will  shortly 
become  transferred  to  the  second,  so  that  the  second  will 
be  swinging  and  the  first  still.  Then  the  second  will  re- 
transfer  its  energy  back  to  the  first,  and  so  they  will  go  on 
until  the  original  energy  given  to  the  first  pendulum  is 
exhausted.  The  point  to  be  observed  is  the  quickness 
with  which  one  pendulum  responds  to  the  impulses  given  it 
by  the  other,  and  the  ease  with  which  the  energy  of  the  one 
passes  to  the  other. 

Now  reduce  the  length  of  one  pendulum.  On  setting  the 
first  in  motion  a  certain  irregular  spasmodic  action  is  to  be 
observed  in  the  second,  but  it  is  very  different  from  the 
"  whole-hearted "  response  in  the  previous  instance.  In 
the  former  case  the  second  one  responded  naturally  and 
readily  to  the  first.  Now  its  response  is  reluctant  in  the 
extreme.  It  moves  somewhat  because  it  is  forced  to,  but 
it  is  apparently  unwilling.  Energy  has  to  be  impressed 
upon  it.  There  is  no  readiness,  because  there  is  no  sympathy 
between  them. 


OF  MODERN  TIMES  161 

That  sympathy  between  the  two  equal  pendulums  is 
"  resonance."  The  same  occurs  between  two  violin  or 
piano  strings  when  they  are  "  in  tune." 

The  explanation  is  that  a  pendulum  has  a  certain  natural 
frequency  which  depends  upon  its  length.  Another  pendulum 
of  the  same  length,  arranged  as  just  described,  therefore 
imparts  impulses  to  it  at  just  the  frequency  which  is  natural 
to  it.  Consequently  the  effect  is  a  cumulative  one,  and  it 
responds  quickly.  Impulses  at  any  other  frequency  tend 
more  or  less  to  neutralise  each  other.  In  the  same  way 
a  string,  of  a  certain  length  and  a  certain  tension,  has  a 
frequency  peculiarly  its  own,  and  it  will  respond  to  another 
similar  string  because  the  other  gives  its  impulses  at  its 
own  natural  frequency. 

It  is  on  record  that  an  engine  in  a  factory  happened  to  run 
at  precisely  the  same  speed  as  the  natural  frequency  of  the 
building,  with  the  result  that  after  a  little  time  the  structure 
shook  so  much  that  it  collapsed. 

Now  electrical  circuits  in  which  currents  oscillate  have  a 
natural  frequency  of  their  own.  That  frequency  depends 
upon  the  two  electrical  properties  of  the  circuit :  capacity 
and  inductance.  And  if  you  want  to  set  up  an  electrical 
oscillation  in  any  circuit  you  can  best  do  it  by  giving  it 
impulses  at  intervals  which  agree  with  its  natural  frequency. 

Sir  Oliver  Lodge  seems  to  have  been  the  first  to  appreciate 
fully  the  effects  of  resonance  in  wireless  telegraphy.  It  is 
strange  that  in  England  the  work  of  this  eminent  man  in 
"  wireless  "  matters  is  not  more  fully  recognised.  When 
wireless  telegraphy  reached  the  point  at  which  the  public 
became  interested,  Marconi  was  just  coming  to  the  front 
and  so,  for  ever,  will  his  name  be  foremost  in  the  public 
estimation.  Indeed  more  than  foremost,  for  in  the  minds 
of  many  he  monopolises  the  credit  for  this  invention. 
Many  people  are  under  the  impression  that  he  is  the  one 
and  only,  or  at  any  rate  the  original,  inventor  of  wireless 
telegraphy. 

Now  Marconi  has  done  exceedingly  valuable  work  in  this 


162  THE  MOST  STRIKING  INVENTION 

field.  Moreover,  he  has  been  the  means  of  placing  the  affair 
on  a  good  commercial  footing.  But  all  the  same  he  is  by  no 
means  the  original  or  only  inventor.  While  admitting  that 
he  is  a  remarkable  man,  who  has  done  wonders,  it  is  only 
common  justice  to  refer  to  the  others  whose  contributions 
to  the  solution  of  the  problem  are  possibly  of  equal  value. 
And,  of  these,  few  can  compare  with  Sir  Oliver  Lodge. 

But  to  return  to  the  question  of  resonance.  At  first  the 
distances  over  which  messages  could  be  sent  were  but  small. 
Now  a  marconigram  can  be  flung  across  a  hemisphere.  At 
first  little  could  be  done  by  day,  work  had  to  be  done 
mainly  at  night.  Now  communication  passes  by  day  and 
night  alike.  Yet  in  principle,  and  in  many  details,  the 
instruments  are  unaltered  from  what  they  were  several 
years  ago.  The  main  source  of  all  this  improvement  is  the 
use  of  resonance. 

To  enumerate  broadly  the  apparatus  used  for  the  dispatch 
and  receipt  of  messages  the  following  list  will  be  useful : — 

Transmitting  End 

(1)  An  Antenna,  consisting  of  a  number  of  wires  raised 

to  a  considerable  height  above  the  ground. 

(2)  A    Spark-gap,  consisting    of  a   series   of  metal    balls 

with  gaps  between  them,  the  outer  ones  being  con- 
nected to  the  antenna  and  to  the  induction  coil. 

(3)  A  powerful    Induction  Coil  with    batteries    or    other 

source  of  current  to  work  it. 

(4)  A  Telegraph  Key,  by  which  the  induction  coil  can  be 

started  and  stopped  at  will. 

Receiving  End 

(1)  An  Antenna  precisely  similar  to  the  other. 

(2)  A  Coherer  or  other  "  oscillation  detector." 

(3)  A   Receiving   Instrument    which    may   be    a    writing 

telegraph  instrument,  a  telephone,  any  of  a  number  of 
ordinary  telegraph  instruments,  or  a  galvanometer. 


OF  MODERN  TIMES  168 

Transmitting  and  sending  instruments  are,  of  course, 
installed  at  both  ends  and  either  of  them  can  be  connected 
to  the  antenna  at  will  by  the  simple  movement  of  a  switch. 

The  antenna  plays  the  part  of  one  of  the  metal  plates  in 
the  Hertz  oscillator.  Early  experiments  were  made  with 
Hertz  apparatus,  but  the  range  of  such  a  contrivance  is  very 
limited.  For  one  thing,  it  neglects  to  take  advantage  of  the 
earth.  It  is  little  realised  what  an  important  part  the  earth 
plays  in  the  carrying  of  wireless  messages.  A  very  great 
step  was  taken  when  Marconi  dispensed  with  one  of  the 
plates  of  Hertz,  and  used  the  earth  instead  ;  w^hile  the 
other  plate  gave  place  to  the  elevated  wires,  the  most 
familiar  part  of  the  apparatus  to  most  people. 

The  condenser  is  thus  formed  by  the  earth  as  one  plate, 
the  elevated  wires  as  the  other,  and  the  intervening  air  as 
the  insulator.  The  "  capacity  "  must  be  exceedingly  small 
in  such  an  apparatus,  but  it  is  sufficient ;  while  the  long 
lines  of  electrical  force  stretching  from  the  high  antenna 
to  the  earth  produce  waves  of  great  carrying  power. 
Lastly,  when  the  earth  forms  a  part  of  the  condenser 
the  waves  cling  to  it,  so  that  instead  of  being  largely  dis- 
sipated into  space,  they  move  along  the  surface  of  the 
earth.  The  advantage  of  this  is  obvious. 

At  first  it  was  customary  to  place  the  spark-gap  in  the 
wire  leading  from  the  antenna  to  the  earth,  as  in  the  accom- 
panying sketch.  Later,  however,  it  was  found  better  to 
place  the  coil  and  spark-gap  in  a  local  circuit  in  which  the 
oscillations  are  first  produced.  These  oscillations  pass 
through  a  coil  which  is  interwound  with  another  one  con- 
nected to  the  antenna  and  to  earth,  and  thus  the  local - 
oscillations,  as  we  might  call  them,  induce  similar  oscillations 
in  the  antenna,  just  as  the  fluctuations  in  one  part  of  an 
induction  coil  induce  fluctuations  in  the  other.  Indeed  the 
coil  in  the  local  circuit  and  the  one  in  the  antenna  circuit 
actually  constitute  an  induction  coil. 

The  advantage  of  this  is  that  by  introducing  condensers 
the  capacity  of  which  can  be  varied,  and  coils  the  inductance 


164  THE  MOST  STRIKING  INVENTION 

of  which  can  be  varied,  into  the  oscillation  circuit  it  becomes 
possible  to  "  tune  "  the  circuits  effectively.  Thus  resonance 
comes  into  play  and  the  power  expended  can  be  made  to 
produce  the  maximum  effect. 

Some  attempts  have  been  made  to  displace  the  induction 
coil  in  wireless  telegraphy  altogether  by  a  specially  made 
dynamo.  These  machines  can  produce  either  alternating  or 
continuous  currents,  in  fact  the  alternating  current  dynamo 
is  really  simpler  than  the  more  familiar 
continuous  -  current  machine.  The 
.,  ,£>  difficulty  is,  however,  to  run  it  suffici- 

ently fast  to  produce  sufficiently  rapid 
alternations.     Nicola   Tesla  made  an 
alternator    (to    give    the    alternating 
current  dynamo  its  short  title)  which 
could    produce  1500    alternations  per 
second,  while   Mr  W.  Duddell  made 
one    which     produced     120,000,    but 
neither  was  satisfactory  for  the  work 
in   question.      Could  such  a  machine 
be  made,  it  would  be  invaluable,  for 
t^^fcT    it  will  be  apparent  that  a  continuous 
"^     ****          succession  of  waves  would  be  formed 
•*/*.""  by  it   and  not  a  succession  of  short 

FIG.  11.— The  simplest  form  trains  of  waves  such  as  is  produced 

of  wireless  antenna.  -         «*        •     -i       «_•  -i  i  -, 

by  the  induction  coil  and  spark-gap. 

The  difficulties  are  not  electrical,  but  mechanical.  It  seems 
doubtful  if  a  machine  will  ever  be  made  to  run  with 
sufficient  rapidity  which  would  not  knock  itself  to  pieces  in 
a  very  short  time. 

Small  alternators  are  used  sometimes,  however,  to  supply 
alternating  current  to  the  primary  of  an  induction  coil,  or 
transformer,  as  it  is  more  often  called  in  its  larger  sizes. 
The  interrupter  is  only  needed  when  the  primary  current 
is  continuous — from  batteries,  for  example.  Alternating 
current  needs  no  interrupter,  and  so  that  bother  is  removed. 
The  alternations  of  a  hundred  or  so  per  second,  which 


OF  MODERN  TIMES  561 

are  quite  the  common  thing  with  alternators,  are  just 
what  is  needed  to  excite  an  induction  coil.  Consequently 
small  machines  of  this  kind  are  to  be  found  in  many 
stations. 

A  Danish  inventor,  Valdemar  Poulsen,  has  adopted  an 
altogether  different  method  of  producing  electrical  oscilla- 
tions, which  method  is  the  distinctive  feature  of  his  mode  of 
telegraphy.  He  takes  advantage  of  a  curious  effect  of  passing 
current  between  two  rods,  one  of  which  is  carbon,  so  as  to 
form  an  arc  such  as  we  see  in  arc  lamps. 

My  readers  are  already  familiar  with  the  term  "  shunt " 
in  connection  with  electrical  matters,  and  so  will  perceive 
at  once  what  is  meant  when  a  second  circuit  is  said  to  be 
arranged  as  a  shunt  to  the  arc.  The  accompanying  diagram 
will  in  any  case  make  the  matter  clear. 

The  current  comes  along  from  the  battery  or  continuous- 
current  dynamo  to  a  hollow  rod  of  copper  which,  to  prevent 
it  being  melted,  has  cold  water  continually  circulating  inside 
it.  Thence  the  current  jumps  across  to  a  carbon  rod,  forming 
an  arc  between  the  two  rods,  and  returns  whence  it  came. 
In  its  journey  it  traverses  the  coils  of  an  electro-magnet, 
the  poles  of  which  are  one  each  side  of  the  arc.  This  tends 
to  blow  the  arc  out,  as  a  puff  of  wind  blows  out  a  candle,  an 
effect  which  a  magnet  always  has  upon  an  electric  arc. 

The  shunt  consists  of  a  wire  leading  from  the  copper  to 
the  carbon  rod  with  a  condenser  and  an  inductance  coil  in- 
serted in  it.  The  latter  coil  also  forms  one  part  of  that  coil 
by  which  the  oscillations  in  the  local  circuit  are  transferred 
to  the  antenna. 

The  electrical  explanation  of  what  happens  when  the 
current  is  turned  on  to  an  arrangement  like  this  is  rather 
too  complex  to  set  out  here.  It  depends  upon  a  curious  be- 
haviour of  the  arc.  It  is  really  a  conductor,  yet  it  does  not 
behave  as  ordinary  conductors  do,  and  the  result  is  that  the 
continuous  current  flowing  through  the  arc  is  accompanied 
by  an  oscillating  current  in  the  shunt  circuit.  And  the  im- 
portant feature  of  the  arrangement  is  that  these  oscillations 


166 


THE  MOST  STRIKING  INVENTION 


are  continuous,  in  one  long  train,  not  in  a  succession  of  trains. 
The  advantage  of  this  has  already  been  referred  to. 

One  other  feature  of  the  apparatus  just  described  should 
be  mentioned,  since  it  will  seem  curious  to  the  general  reader. 
For  it  to  work  properly  it  is  necessary  that  the  arc  should  be 
enclosed  in  a  chamber  filled  with  hydrogen  or  a  hydro-carbon 
gas.  Coal-gas  is  generally  used. 

Hertz'  original  discovery  was  that  small  sparks  could  be 
seen  to  pass  between  the  ends  of  a  curved  wire  when  the 


FIG.  12.— Diagram  (simplified)  showing  how  Poulsen  generates  oscillations. 
Current  from  a  dynamo  flows  through  the  arc,  whereupon  currents  oscillate 
through  the  condenser  and  coil  (as  described  in  the  text). 

electric  waves  fell  upon  it.  Such  "  spark  detectors,"  as  they 
are  called,  are  useful  in  the  laboratory,  but  not  for  practical 
telegraphy. 

Several  people  seem  to  have  noticed  in  years  gone  by  that 
a  mass  of  loose  metal  filings,  normally  a  very  bad  conductor 
of  electricity,  became  a  much  better  conductor  when  an 
electrical  discharge  of  some  sort  occurred  near  by.  The 
demand  for  a  wireless  receiver  had  not  then  arisen,  however, 
and  so  the  discoveries  were  not  followed  up.  Consequently 
it  remained  to  be  rediscovered  by  Branly,  of  Paris,  in  1890. 
He  placed  some  metal  filings  in  a  glass  tube,  the  ends  of  which 


OF  MODERN  TIMES  167 

he  closed  with  metal  plugs.  Lying  loosely  together  the  filings 
would  not  conduct  the  current  of  a  small  battery  from  one 
plug  to  the  other,  but  when  a  spark  occurred  not  far  away 
they  suddenly  became  conductive  and  allowed  it  to  pass. 
Several  years  after  this  Sir  Oliver  Lodge  took  up  the  idea  as 
a  receiver  for  wireless  messages,  and  believing  that  its  action 
was  due  to  the  waves  causing  the  filings  to  cling  together,  he 
christened  it  "  Coherer." 

Marconi  succeeded  in  making  a  very  delicate  form  of  this, 
although  working  on  strictly  the  same  lines. 

The  trouble  with  a  coherer  is  that  when  once  it  becomes 
conductive  it  remains  so  unless  the  filings  be  shaken  apart. 
Lodge  therefore  arranged  for  the  tube  to  be  continually 
struck  by  clockwork  or  by  a  mechanism  like  that  of  an  electric 
bell.  Marconi  effected  a  further  improvement  by  making 
the  current  passing  through  the  coherer  control  the  striking 
mechanism,  so  that  the  latter  is  normally  quiet  but  administers 
one  or  two  taps  at  just  the  right  moment. 

Sir  Oliver  Lodge  and  Dr  Muirhead  devised  another  de- 
tector which,  though  quite  different  in  form,  is  really  much 
the  same  in  principle.  A  steel  disc  with  a  sharp  knife-like 
edge  is  made  to  rotate  above  a  vessel  of  mercury.  The  edge 
just  touches  the  mercury  but  no  more.  On  the  top  of  the 
mercury  there  floats  a  thin  layer  of  oil,  a  bad  conductor. 
Now  as  the  disc  revolves  it  picks  up  on  its  edge  a  film  of  oil, 
which  it  carries  down  into  the  mercury.  The  film  adheres 
so  tightly  that  it  prevents  the  moving  disc  from  actually 
touching  the  liquid  metal.  Thus,  under  normal  conditions, 
the  two  are  electrically  insulated  from  each  other  by  the  film 
of  oil  and  no  current  can  pass  from  mercury  to  disc.  Oscilla- 
tions, however,  caused  by  incoming  electric  waves,  are  able 
to  break  through  the  oil  film  and  so  bring  disc  and  mercury 
into  contact,  whereupon  the  current  flows.  The  constant 
movement  of  the  disc  restores  the  oil-film  as  soon  as  the 
oscillations  cease. 

The  reason  why  these  detectors  act  as  they  do  is  not  quite 
understood.  One  suggested  explanation  is  that  the  oscillating 


168  THE  MOST  STRIKING  INVENTION 

currents  heat  the  particles  and  so  partially  weld  them 
together.  Another  is  that  adjacent  particles  become  charged 
as  the  plates  of  a  minute  condenser,  and  so  are  drawn  tightly 
together  as  the  plates  in  an  electrostatic  voltmeter  are 
drawn  towards  each  other.  Supposing  that  the  original  non- 
conductivity  of  the  loose  filings  be  due  to  the  film  of  air  which 
may  surround  them,  either  of  these  things  would  account  for 
the  film  being  broken  or  squeezed  out,  resulting  in  better 
contact  and  improved  conducting  power.  But  both  sug- 
gestions seem  to  be  contradicted  by  the  fact  that  if  the  pieces 
in  contact  be  of  certain  substances  the  coherer  works  the 
opposite  way.  Under  those  conditions  the  conductivity  is 
normally  good,  but  the  influence  of  the  incoming  waves 
causes  it  to  become  bad. 

In  1896  Professor  Rutherford,  now  of  Manchester,  described 
some  discoveries  which  he  had  made  as  to  the  magnetic 
effects  of  oscillations.  A  simple  little  contrivance  which  he 
had  constructed  was  operated  by  the  discharge  of  a  coil  half- 
a-mile  away,  at  that  time  a  great  performance.  This  de- 
tector was  simply  an  electro-magnet  with  a  steel  core  instead 
of  the  usual  soft  iron  core.  The  reason  the  latter  is  used 
in  the  ordinary  magnet  is  that  it  loses  its  magnetism  the 
moment  the  current  ceases  to  pass  through  the  coil  with 
which  it  is  surrounded,  while  a  steel  core  retains  its  magnet- 
ism. For  most  purposes  a  steel  core  would  render  an  electro- 
magnet useless,  but  in  this  case  it  was  desired  that  the  core 
should  be  permanently  magnetised.  So  a  current  was  first 
passed  through  the  coil  to  magnetise  the  core,  and  then  the 
coil  was  connected  to  a  simple  form  of  antenna  while  a 
swinging  magnet  was  brought  near  so  that  the  magnetic 
power  of  the  core  would  be  indicated  and  any  change  made 
apparent.  The  effect  of  the  discharge  half-a-mile  away  was 
to  demagnetise  the  core  slightly.  This  was  shown  by  the 
movement  of  the  swinging  magnet,  and  so  the  first  "  mag- 
netic detector  "  was  found. 

But  here,  perhaps,  I  ought  to  explain  the  use  of  the 
antenna  at  the  receiving  station — its  function  at  the  sending 


OF  MODERN  TIMES  169 

end  has  already  been  made  clear.  The  electro-magnetic 
waves,  coming  from  the  distant  transmitter,  strike  the  re- 
ceiving antenna  and  in  so  doing  set  up  in  it  oscillations  such 
as  those  which  set  them  in  motion.  For  every  oscillation  in 
the  sending  antenna  there  will  be  another,  similar  in  every 
respect  except  that  it  will  be  feebler,  in  the  receiving  antenna. 
And  the  oscillations  are  here  led  to  the  detector,  of  whatever 
form  it  may  be,  and  in  it  they  make  their  presence  felt. 

In  some  few  cases  a  Duddell  thermo-galvanometer  has  been 
employed  as  the  detector,  in  which  the  oscillating  currents 
report  themselves  directly.  In  coherers  the  detector  works 
by  causing  the  oscillating  currents  to  control  a  continuous 
current  from  a  battery  and  it  is  the  latter  which  actually 
gives  the  signal,  but  there  are  a  number  of  extremely 
interesting  means  which  have  been  invented  to  detect 
the  oscillating  currents  by  their  heating  effect. 

R.  A.  Fessenden,  for  instance,  has  perfected  one  which  is 
a  marvel  of  delicate  workmanship.  He  depends  upon  the 
heating  of  a  wire  by  the  currents  passing  through  it.  Such 
heating  is  the  result  of  the  electrical  force  acting  against 
resistance,  and  the  difficulty  is  that  if  the  resistance  be  great 
it  will  almost  entirely  kill  the  faint  oscillating  forces  in  the 
receiving  antenna,  while  if,  on  the  other  hand,  it  be  small, 
the  rise  in  temperature  will  be  inappreciable.  So  he  encloses 
a  fine  thread  of  platinum  in  a  glass  bulb  from  which  the  air 
is  exhausted.  The  platinum  wire  is  first  of  all  embedded  in 
a  wire  of  silver  :  the  silver  wire  is  given  a  core  of  platinum,  in 
fact.  Then  the  compound  wire  is  drawn  down  until  it  is  so 
thin  that  the  platinum  core  is  only  one  and  a  half  thousandths 
of  an  inch  in  diameter.  A  short  length  of  this  compound 
wire  is  then  bent  into  a  U-shaped  loop  and  its  ends  connected 
to  thicker  wires.  Finally  the  bottom  of  the  loop  is  im- 
mersed in  nitric  acid,  which  eats  away  the  silver  at  that  point 
and  leaves  the  bare  platinum.  Thus  is  produced  a  very 
short  length  (a  few  millimetres)  of  exceedingly  thin  platinum 
wire  supported  at  its  ends  by  comparatively  thick  wires. 

Being  so  short,  this  wire  does  not  offer  much  resistance,  and 


170  THE  MOST  STRIKING  INVENTION 

consequently  does  not  materially  check  the  oscillations. 
At  the  same  time,  since  it  is  so  fine,  it  does  offer  some  resist- 
ance, and  finally,  since  what  heat  is  generated  will  be  in  an 
exceedingly  small  space,  it  will  be  appreciable  there.  A 
telephone  is  arranged  so  that  its  current  also  passes  through 
the  fine  wire,  and  every  slight  variation  in  the  temperature 
of  the  platinum  wire,  by  varying  its  resistance,  varies  the 
current  through  the  telephone.  And  exceedingly  slight 
variations  can  be  detected  by  sound  in  the  telephone.  Thus 
the  oscillations  generated  in  the  antenna  affect  the  heat  in 
the  wire ;  that  affects  its  resistance ;  and  that  again  affects 
the  telephone,  which,  finally,  affects  the  ear  of  anyone  who  is 
listening  to  it.  It  must  be  understood,  however,  that  this 
is  not  a  wireless  telephone,  for  the  sounds  heard  are  not 
articulate  but  merely  long  and  short  sounds,  representing  the 
dots  and  dashes  of  the  "  Morse  Code." 

Electrolysis  provides  us  with  another  form  of  detector. 
An  exceedingly  small  platinum  wire  forms  one  electrode  and 
a  large  lead  plate  the  other,  and  both  are  immersed  in  dilute 
acid.  The  passage  of  current  from  a  local  battery  sets  up 
electrolysis,  and  so  stops  itself  by  forming  a  film  of  oxygen 
on  the  small  electrode.  This  film,  however,  is  broken  by  the 
oscillating  currents  from  the  antenna,  so  that  as  long  as  they 
are  coming  the  battery  current  can  flow,  but  as  soon  as  they 
cease  the  battery  current  stops  itself  again.  Thus  the  flow- 
ing and  stopping  of  the  oscillating  currents  is  exactly  copied 
by  the  current  from  the  battery,  which  current  is  led  through 
a  telephone  or  a  sensitive  galvanometer. 

It  may  occur  to  readers  to  inquire  why  the  oscillating 
currents  are  not  passed  direct  to  a  galvanometer.  The 
answer  is  that  because  they  are  oscillating  a  very  sensitive 
galvanometer  is  not  possible. 

True,  the  Duddell  thermo-galvanometer  has  been  men- 
tioned in  this  connection,  but  although  it  is  a  beautiful  instru- 
ment it  cannot  compare  for  delicacy  with  the  direct-current 
galvanometers.  The  latter  are  easily  a  hundred  thousand 
times  more  sensitive.  But  the  trouble  can  be  overcome  by 


OF  MODERN  TIMES  171 

"rectifying"  the  oscillating  currents, by  passing  them  through 
a  "  unidirectional "  conductor — one,  that  is,  which  passes 
current  one  way  only.  These  remind  one  of  a  turnstile  as  in- 
stalled at  certain  public  places,  which  let  you  out  but  will 
not  let  you  in  unless  you  pay.  In  fact  they  will  not  let  you 
in  at  all.  In  like  manner  "  rectifiers  "  will  only  allow  those 
currents  to  pass  which  are  flowing  in  one  direction,  and  so 
they  cut  out  every  alternate  oscillation,  thus  producing  some- 
thing very  like  continuous  current,  which  can  be  detected  by 
the  very  delicate  galvanometers  which  are  usable  where 
continuous  currents  are  concerned,  or  more  often  by  a  tele- 
phone receiver.  The  rectifying  conductors  are  in  many  cases 
crystals,  hence  these  detectors  are  called  "  Crystal  Detectors." 
Carborundum  is  a  favourite  for  this  purpose. 

And  that  brings  us  to  the  important  question  of  the  secrecy 
of  wireless  communication,  and  the  measures  taken  to  pre- 
vent confusion  from  the  number  of  independent  messages 
flying  through  the  air  at  the  same  time. 

This  can  be  largely  achieved  by  the  aid  of  resonance. 
Trains  of  waves  flung  out  by  one  antenna  may  strike  several 
other  antennae,  but  unless  the  latter  are  in  tune  with  the 
sending  apparatus  they  will  probably  not  be  affected  appreci- 
ably. Let  one  of  them,  however,  be  in  tune,  and  it  will  pick 
up  easily  the  message  which  is  not  noticed  by  the  others. 
It  is  as  if  three  people  watching  a  distant  lamp  were  affected 
by  a  form  of  colour-blindness  which  rendered  them  practically 
blind  to  all  colours  except  one.  Suppose  one  could  see  red 
only,  the  other  blue  and  the  third  yellow.  A  light  sent 
through  a  blue  glass  being  robbed  of  all  rays  except  the  blue 
ones  would  be  visible  only  to  the  man  who  could  see  blue. 
The  man  who  could  see  blue  would,  in  like  manner,  be  quite 
blind  to  light  sent  through  red  or  yellow  glass.  Each  of  them, 
in  fact,  could  be  signalled  to  quite  independently  of  the 
others  by  simply  sending  him  rays  of  the  colour  to  which  his 
eyes  were  sensitive.  In  precisely  the  same  way  each  wireless 
receiver  is  or  can  be  made  most  sensitive  to  waves  of  a 
particular  length  and  practically  blind  to  all  others.  The 


172  THE  MOST  STRIKING  INVENTION 

operator  can  adjust  his  apparatus  for  certain  prearranged 
wave-lengths,  and  so  he  can  communicate  with  secrecy  to 
stations  whose  wave-length  he  knows.  The  change,  of  course, 
is  made  by  altering  the  capacity,  or  inductance,  or  both. 
The  instruments  can  be  so  calibrated  that  it  is  quite  easy  to 
make  the  alteration. 

Then,  antennae  can  be  so  constructed  that  messages  can  be 
received  with  most  readiness  from  one  particular  direction. 
In  others,  they  can  be  received  from  any  direction,  but  the 
direction  can  be  discovered.  This,  it  will  be  easy  to  see,  is 
of  great  value  to  ships  in  a  fog. 

Antennae  made  with  a  short  vertical  part  and  a  long  hori- 
zontal part  radiate  best  in  the  direction  away  from  which 
their  horizontal  part  points.  This  is  of  great  advantage  in 
stations  which  are  built  specially  to  communicate  with  other 
particular  stations.  In  such  cases  the  antenna  is  carefully 
built,  so  as  to  point  in  the  required  direction.  Such  antennae 
also  receive  more  readily  those  signals  which  come  from  the 
direction  away  from  which  they  are  pointing. 

Reference  has  been  made  already  to  the  interesting  fact 
that  wireless  communication  is  easier  at  night  than  in  the 
daytime.  That  is  probably  because  of  the  "  ionisation  "  of 
the  atmosphere  by  the  action  of  sunlight.  Along  with  the 
visible  sunlight  there  comes  to  us  from  the  sun  a  quantity 
of  light  known  as  ''ultra-violet,"  since  it  makes  its  effect 
known  in  the  spectrum  of  sunlight  beyond  the  violet,  which 
is  the  limit  of  visibility  at  one  end  of  the  spectrum.  We 
cannot  see  it  but  it  affects  photographic  plates  powerfully. 
It  has  energetic  chemical  powers,  and  it  has  the  ability  to 
make  the  air  more  conductive  than  it  is  ordinarily.  Com- 
paratively little  of  it  penetrates  our  atmosphere,  but  it  must 
exercise  a  good  deal  of  influence  a  little  higher  up.  Now 
readers  will  remember  that  the  process  by  which  electro- 
magnetic waves  are  propagated  is  checked  when  the  waves 
strike  a  conductor.  The  energy  in  the  waves  is  then  em- 
ployed in  causing  currents  in  the  conductor  instead  of  form- 
ing more  waves.  And  so  partially  conductive  air  forms  a 


OF  MODERN  TIMES  173 

partial  barrier  to  the  waves.  The  effect  is  not  appreciable 
in  the  case  of  the  tiny  waves  of  light  and  heat,  but  it  is  in  the 
case  of  the  long  "  wireless  waves."  Everyone  has  seen  the 
waves  of  an  advancing  tide  coming  up  a  sandy  beach,  and  has 
noticed  how  the  dry  sand  (a  good  conductor  of  water)  sucks 
up  and  destroys  the  foremost  ripples.  In  like  manner  are 
the  wireless  waves  "  sucked  up  "  by  the  partially  conductive 
atmosphere.  But  the  effect  of  the  ultra-violet  light  does  not 
last  long,  and  so,  at  night-time,  it  disappears.  Therefore 
messages  can  be  sent  better  at  night  than  by  day. 

For  wireless  telephony  what  is  wanted  is  a  continuous  un- 
interrupted train  of  waves,  such  as  those  from  the  "  Poulsen 
arc,"  and  a  receiver  of  the  magnetic  type.  The  coherer  is 
no  good  for  this  purpose,  since  it  either  stops  the  current 
entirely  or  lets  it  flow  copiously.  The  magnetic  detectors, 
liowfever,  respond  to  the  variations  in  the  strength  of  the  in- 
coming waves.  As  the  latter  increase  or  decrease  in  strength 
so  does  the  magnetic  detector  give  out  stronger  or  weaker 
signals.  So  a  telephone  transmitter  of  the  ordinary  type  is 
made  to  vary  the  strength  of  the  oscillations  at  the  sending 
end,  while  an  ordinary  telephone  receiver  is  placed  in  series 
with  the  detector  at  the  receiving  end.  Thus  every  slight 
variation  corresponding  to  sound  waves  spoken  into  the 
transmitter  is  reproduced  in  the  receiver. 

It  is  strange  that  wireless  telephony  has  not  made  greater 
progress,  for  it  may  be  said,  on  the  word  of  one  of  the  greatest 
authorities,  that  wireless  telephony  is  simpler  and  easier  than 
telephony  through  a  submarine  cable.  In  the  latter  there  are 
almost  insuperable  obstacles  caused  by  the  capacity  and  in- 
ductance of  the  circuit,  while  in  the  wireless  method  there 
is  very  little  difficulty. 

There  are,  of  course,  several  so-called  "  systems  "  of  wire- 
less telegraphy  in  use.  There  is  the  Marconi  in  Great 
Britain ;  the  secret  Admiralty  system  in  the  British  Navy ; 
the  De  Forest  in  the  United  States;  the  Telefunken  in 
Germany,  not  to  mention  the  promising  Poulsen  system. 
And  there  are  still  others,  But  it  would  be  futile  to  attempt 


174  THE  MOST  STRIKING  INVENTION 

to  explain  how  they  differ  from  one  another  in  a  work  like 
this.  In  principle  they  are  alike.  The  precise  forms  of 
instrument  used  may  vary,  but  even  there  there  is  much  in 
common  between  them.  As  time  goes  on  there  will  in- 
evitably be  a  tendency  to  more  and  more  uniformity.  That 
is  always  the  case,  for  some  things  are  inherently  better  than 
others,  and  rival  systems,  although  each  is  working  along  its 
own  lines,  always  come  to  very  much  the  same  result  in  the 
end.  Without  making  any  comparisons,  it  is  safe  to  say 
that  if  the  Telefunken  system,  for  example,  has  any  points 
of  superiority  over  the  Marconi,  the  latter  will  sooner  or 
later  find  out  the  fact,  and  will  modify  their  apparatus 
accordingly.  In  all  probability  this  will  operate  both  ways, 
and  some  things  which  the  German  system  is  now  using 
will  give  place  to  those  which  the  British  have  in  operation. 

In  another  very  modern  industry  this  is  very  apparent. 
Having  attended  and  carefully  studied  several  annual 
exhibitions  of  flying  machines,  I  have  noticed  with  great 
interest  how  the  varying  types  of  a  few  years  ago  are  merging 
into  the  more  or  less  uniform  types  of  to-day.  And  it  has 
been  the  same  with  wireless  telegraphy,  and  will  be  still 
more  so  in  the  future. 

The  best  means  of  generating  the  waves  and  the  best 
means  of  detecting  them  at  a  distance — that  is  the  whole 
problem,  and  all  the  workers  in  it  will  sooner  or  later  come 
to  much  the  same  conclusions  as  to  which  are  the  best 
ways. 

Patents  may  do  a  little  to  delay  this,  but  not  much.  For 
one  thing,  patents  only  last  a  few  years.  For  another,  a 
patent  only  covers  a  particular  way  of  doing  a  particular 
thing.  A  machine  that  is  termed  "  patent "  is  often  the 
subject  of  a  hundred  patents,  each  covering  a  particular 
little  point.  It  is  well-nigh  impossible  to  patent  a  whole 
machine.  A  general  principle  cannot  be  patented,  only  a 
particular  application  of  that  principle,  and  so  there  are  in 
a  great  many  cases  little  variations  of  a  patented  method 
which  are  quite  as  good  as  the  patented  one,  and  which  can 


OF  MODERN  TIMES  175 

be  used  freely.     So  even  patents  will  not  have  much  effect, 
in  all  probability,  upon  this  unification  process. 

But,  however  that  may  be,  there  is  no  doubt  that  the 
whole  world  owes  a  deep  debt  of  gratitude  to  the  men  who 
have  worked  out  this  most  beneficent  of  inventions.  It  is 
difficult  to  think  of  a  single  one  which  has  ever  brought  such 
a  load  of  benefits  to  poor,  struggling  humanity  as  this  has. 
The  ship  in  distress,  the  lighthouse  man  on  his  lonely  islet, 
the  explorer  in  the  Polar  regions,  the  pioneer  settler  in  the 
new  lands — in  fact,  just  those  who  most  need  some  connecting 
link  with  their  fellows — are  the  people  to  whom  the  wireless 
telegraph  brings  aid  and  comfort.  All  honour  to  the  men 
who  have  done  it. 


CHAPTER  XIII 

HOW  PICTURES   CAN  BE  SENT  BY  WIRE 

THE  sending  of  a  message  by  telegraph  is  easily 
understandable.  Various  combinations  of  two 
simple  signs,  such  as  short  sounds  and  long  sounds, 
can  readily  be  made  to  indicate  letters  by  which  the  words 
can  be  spelt  out. 

Nor  does  the  sending  of  sound  over  a  wire  make  a  very 
great  demand  upon  the  credulity.  We  all  know  that  sound 
consists  of  innumerable  little  waves  in  the  air,  and  by  the 
simplest  of  devices  these  can  be  converted  into  variations 
in  an  electric  current,  which  variations,  by  means  equally 
simple,  can  be  made  to  re-convert  themselves  back  into 
sound  waves  at  the  other  end. 

But  to  transmit  a  picture  is  another  matter  altogether. 
It  seems  barely  possible  in  the  case  of  a  drawing  such  as  a 
pen-and-ink  sketch,  which  consists  of  a  comparatively  small 
number  of  definite  lines  ;  but  with  a  shaded  sketch  or  a 
photograph,  with  its  gradations  of  light  and  shadow — to 
transmit  such  would  seem  to  be  beyond  the  bounds  of 
possibility,  did  we  not  know  that  it  has  been  done.  The 
description  of  the  methods  will  therefore  constitute  a  not 
uninteresting  subject  for  a  chapter. 

It  is  worthy  of  remark  that  an  attempt  along  these  lines 
was  made  many  years  ago  by  a  man  named  Caselli,  and  a 
description  of  this  pioneer  apparatus  will  form  a  good 
introduction  to  the  later  developments. 

In  Fig.  13  we  see  a  square  which  represents  a  sheet  of  tin- 
foil, upon  which  is  drawn,  in  non- conductive  ink,  a  simple 
geometrical  figure.  The  ink  may  be  grease,  or  shellac  varnish, 
indeed  there  are  many  substances  which  are  available  for 

176 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE    177 

use  as  an  insulating  ink.  Across  the  square  there  are  a 
number  of  parallel  dotted  lines,  but  these,  it  must  be  under- 
stood, are  not  actually  drawn  upon  the  foil — their  purpose 
will  be  apparent  in  a  moment. 

Suppose  that  we  connect  the  foil  to  one  pole  of  a  battery, 
and  the  other  pole  by  a  flexible  wire  to  a  "metal  pen  or  stylus. 
If  we  place  the  point  of  the  pen  in  contact  with  the  foil,  we 
make  a  complete  circuit,  through  which,  of  course,  current 


FIG.  13 


FIG.  14 


will  flow.  But  if,  with  it,  we  touch  one  of  the  non-conductive 
lines,  there  will  be  no  current. 

Taking  a  ruler,  then,  let  us  draw  the  point  of  the  stylus 
across  the  foil  in  a  series  of  parallel  straight  lines.  It  is 
these  excursions  of  the  stylus  which  the  dotted  lines  are 
intended  to  represent.  For  nearly  the  whole  of  the  time 
current  will  be  flowing  ;  but  whenever  the  stylus  is  crossing 
one  of  the  lines  of  non-conductive  ink  there  will  be  a  momen- 
tary cessation.  Thus,  the  reader  will  begin  to  perceive, 
we  obtain  what  we  may  call  an  electrical  representation  of 
the  figure  drawn  upon  the  foil. 

And  now  let  us  turn  to  Fig.  14.  There,  too,  is  a  square, 
but  in  this  case  it  is  not  foil,  but  paper  which  has  been  soaked 
in  prussiate  of  potash.  The  reason  for  introducing  this 
chemical  is  that  it  is  susceptible  to  electrical  action.  Where- 
ever  current  passes  through  it,  it  becomes  changed  into 


178    HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

Prussian  blue,  so  that  if  we  place  the  point  of  a  pen  upon  the 
paper,  and  cause  current  to  flow  out  of  that  point  through 
the  paper,  there  we  get  a  blue  dot.  If,  while  the  current  is 
flowing,  we  draw  the  pen  along,  we  get  a  blue  line. 

Fig.  13  therefore  represents  in  principle  the  sending 
apparatus  of  Caselli's  writing  telegraph,  while  Fig.  14 
represents  the  receiving  instrument.  The  two  pens  are 
connected  together  by  the  main  wire,  in  such  a  manner  that, 
when  the  point  of  the  one  is  in  contact  with  the  bare  foil 
current  flows  out  of  the  other  and  into  the  paper  ;  but  as 
the  former  crosses  an  ink  line  all  current  ceases. 

If,  then,  while  the  sending  pen  is  drawn  line  by  line  across 
the  foil,  the  other  is  drawn  at  the  same  speed,  line  by  line, 
across  the  chemically  prepared  paper,  we  shall  get  on  the 
latter  a  series  of  lines  as  shown  in  Fig.  14  almost  continuous, 
but  broken  here  and  there.  Each  breakage  represents  a 
passage  of  the  sending  pen  across  a  line,  and  taken  together, 
as  will  be  seen,  they  constitute  a  reproduction  of  the  geo- 
metrical figure  drawn  upon  the  foil.  As  shown,  the  lines  are 
rather  far  apart,  and  so  the  reproduction  is  not  a  very  good 
one.  They  are  only  drawn  so,  however,  in  order  that  the 
principle  may  be  shown  the  more  clearly.  They  may  be 
drawn  so  that  they  overlap,  and  then  the  effect  is  very  much 
better,  the  received  picture  being  almost  an  exact  reproduc- 
tion of  the  other. 

It  will  be  noticed  that  an  essential  to  the  success  of 
this  method  is  that  the  two  pens  should  move  in  perfect 
unison,  and  that  was  the  great  difficulty.  Caselli  used  an 
arrangement  of  pendulums,  the  best  thing  available  at  the 
time. 

The  reproduction  is,  in  photographic  language,  a  negative, 
a  somewhat  unsatisfactory  feature  of  the  method.  A  simple 
modification,  however,  of  the  electrical  connections  will 
reverse  that,  so  that  the  reproduction  shall  be  a  positive. 
There  are  two  ways  of  cutting  off  a  current  from  any  par- 
ticular circuit.  One  is  to  interpose  a  resistance,  through 
which  current  cannot  pass  in  an  appreciable  quantity,  and 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE    179 

the  other  is  to  provide  a,  second  path  for  the  current  so 
much  easier  than  the  first  that  practically  all  the  current 
will  pass  that  way,  leaving  the  first  circuit,  to  all  intents  and 
purposes,  free.  It  is  as  if  a  farmer  wished  to  stop  people 
passing  across  a  certain  field.  Two  methods  would  be  open 
to  him  :  one  to  put  up  a  high  gate  over  which  no  one  would 
dare  to  climb,  and  the  other  to  provide  a  short  cut  so  much 
more  pleasant  and  convenient  than  the  old  path  that  no 
one  having  the  choice  of  the  two  ways  would  think  of  going 
the  old  way. 

What  the  farmer  would  call  a  short  cut  the  electrician 
calls  a  short  circuit,  and  a  short  circuit  is  often  a  more  con- 
venient way  of  cutting  off  a  current  than  a  switch  which 
interposes  resistance.  At  all  events,  in  a  case  like  this,  a 
short  circuit  enables  that  to  be  accomplished  which  would 
be  very  difficult  by  any  other  means. 

In  the  apparatus  as  already  described  the  battery  had 
to  drive  the  current  along  a  long  wire,  terminating  at  the 
distant  receiving  instrument,  whence  the  current  returned 
via  the  earth.  The  foil  and  pen,  acting  as  a  kind  of  electrical 
"  tap,"  controlled  this.  When  foil  and  pen  touched,  the 
tap  was  open  and  current  flowed.  When  the  line  of  non- 
conductive  ink  interposed  itself,  the  tap  was  off  and  the 
flow  ceased. 

But  connect  the  battery  directly  to  the  wire,  and  place 
the  foil  and  pen  in  a  short  branch  circuit,  and  the  whole 
thing  is  reversed.  Then  the  opening  of  the  "  tap  "  sent 
current  to  the  other  end ;  now  the  opening  of  the  tap  causes 
it  to  flow  round  the  short  branch  and  leave  the  main  wire. 
Then  the  closing  of  the  tap  stopped  the  current  reaching 
the  farther  end  ;  now  it  causes  it  to  do  so.  In  fact,  the 
entire  action  of  the  apparatus  is  completely  reversed,  and 
the  bare  parts  of  the  foil  become  represented  by  blank 
paper,  while  the  insulating  lines  produce  the  marks.  In 
short,  a  positive  results  instead  of  a  negative. 

Such  was  the  scheme  of  Caselli  years  ago.  It  is  mentioned 
here  at  some  length,  since  the  principle  of  it  is  largely  re-used 


180    HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

in  an  improved  form  in  the  most  successful  of  modern 
apparatus  for  a  like  purpose. 

It  undoubtedly  was  a  very  excellent  scheme,  simple  and 
effective,  which  ought  to  have  succeeded  ;  but  it  did  not 
do  so,  for  the  sufficient  reason  that  at  that  time  knowledge 
of  electricity  and  skill  in  constructing  delicate  mechanism 
were  not  so  highly  developed  as  they  are  to-day.  For 
success,  as  has  already  been  said,  one  thing  was  essential, 
and  that  thing  very  difficult  to  obtain — a  perfect  synchronism 
between  one  stylus  and  the  other.  If  the  one  were  but  the 
slightest  degree  "  out  of  step "  with  the  other,  failure 
followed  inevitably. 

So  the  electrical  transmission  of  sketches  dropped  for  the 
time  being.  More  recently  a  perfectly  successful  solution 
of  the  problem  has  come  in  another  way  altogether.  This 
apparatus,  at  first  called  the  telautograph,  but  now  known 
as  the  telewriter,  it  will  be  more  convenient  to  refer  to  later. 

Of  modern  systems  for  the  transmission  of  pictures  the 
most  successful,  probably,  are  the  Korn  telautograph  and 
the  Thorn-Baker  telectrograph. 

Both  of  these  are  able  to  transmit  very  fair  reproductions 
of  photographs  besides  line  drawings.  The  difficulty  with 
photographs  is,  of  course,  that  many  parts  of  them  are  not 
of  equal  blackness  or  whiteness,  but  shade  off  gradually 
from  one  into  the  other.  Take  the  case  of  a  simple  portrait. 
Part  of  the  subject's  face  will  be  pure  white,  while  the  side 
in  shadow  will  be  comparatively  dark.  There  is  no  hard  and 
fast  line  between  the  two,  but  by  a  gradation  through  an 
infinite  number  of  shades  the  one  tones  into  the  other. 
How  can  it  be  possible  to  convey  that,  more  or  less  mechani- 
cally, over  a  wire  ?  The  solution  is  due  to  the  fact  that  the 
eye  will  blend  together  a  number  of  distinctly  different 
shades,  if  properly  arranged,  into  a  gradual  change.  Really 
the  change  is  step  by  step,  but  the  effect  is  apparently  quite 
continuous.  This  can  be  seen  in  the  "  half-tone  "  illustra- 
tions in  this  book.  Close  examination  will  show  that  such 
a  picture  is  cut  up  into  small  squares.  In  the  pure  white 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE    181 

part  the  squares  are  invisible,  while  in  the  perfectly  black 
parts,  if  there  be  any,  they  are  so  merged  into  one  another 
as  to  be  inseparable.  But  everywhere  else  in  the  picture 
it  will  be  seen  that  there  are  squares  each  with  a  dot  in  the 
middle.  In  the  darker  parts  the  dots  are  large ;  in  the  lighter 
ones  they  are  small.  We  get  the  effect  almost  of  colour, 
although  the  picture  is  done  entirely  in  black  ink.  The  eye 
does  not  see  the  individual  dots  when  we  are  just  looking  at 
the  picture ;  we  have  to  examine  it  very  closely  to  find  them. 
Yet  they  are  there  all  the  time,  and  it  is  simply  the  peculiar 
action  of  the  eye  which  sees  beautiful  half-tones,  shading 
imperceptibly  one  into  another,  whereas  in  real  fact  there 
are  only  a  vast  number  of  equidistant  dots,  all  equally  black. 

We  see>  therefore,  that  it  is  possible  to  split  up  a  picture 
of  any  kind  into  a  number  of  small  squares  and  to  treat  each 
square  as  being  of  equal  darkness  throughout.  Then,  if  we 
can  communicate  by  wire  that  particular  degree  of  darkness 
to  a  distant  station,  where  the  small  parts  can  be  put  to- 
gether in  their  proper  order  and  given  their  correct  shade, 
the  picture  as  constructed  at  the  receiving  end  will  be  some- 
thing like  that  at  the  sending  end.  And  we  have  only  to 
make  the  size  of  each  separate  square  small  enough  to  obtain 
a  copy  which  will  resemble  the  original  very  closely  indeed. 

In  the  early  days  it  was  actually  proposed  to  telegraph 
pictures  by  ordinary  telegraphy,  using  this  principle.  The 
suggestion  was  to  agree  upon  a  code  of  twenty-six  shades, 
each  called  by  a  letter  of  the  alphabet.  One  shade  was  to 
be  a,  the  next  6,  and  so  on.  Then  the  picture  was  to  be 
divided  up  into  squares,  and  the  particular  shade  of  each 
square  telegraphed  by  means  of  the  corresponding  letter. 
The  shades  thus  communicated  were  to  be  put  together  at 
the  receiving  end,  on  a  prearranged  system,  and  so  the 
picture  was  to  be  built  up.  Given  plenty  of  time,  that 
scheme  might  be  moderately  successful,  but  to  get  a  really 
good  reproduction  the  subdivision  needs  to  be  so  minute, 
and  the  number  of  squares,  therefore,  so  immense,  that  it 
would  be  quicker  to  send  the  picture  by  train  than  to 


182     HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

telegraph  it  by  such  laborious  means.  In  a  fairly  coarse 
half-tone  block  the  squares  are,  say,  2500  to  the  square  inch. 
That  number  of  letters  would  therefore  have  to  be  tele- 
graphed for  every  square  inch  of  picture  transmitted,  to 
say  nothing  of  the  difficulty  of  building  up  a  picture  of  such 
a  great  number  of  parts  and  giving  to  each  the  desired  shade. 
That  idea,  abortive  though  it  is  in  its  crude  form,  illustrates 
very  clearly  the  fundamental  principle  on  which  this  work 
is  done. 

The  problem  is  really  to  devise  a  machine  which  will  do 
that  same  thing  rapidly  and  automatically  divide  up  the 
original  into  a  large  number  of  squares,  and  then  send  an 
electric  current  to  represent  each  square,  such  current  by 
its  strength  to  indicate  the  shade  of  the  square  :  and  finally 
a  similar  instrument  is  needed  to  act  as  receiver,  and  to 
reproduce  those  squares  in  the  proper  order,  giving  to  each 
its  correct  shade. 

In  practically  all  of  them  the  mechanism  is  rotatory,  the 
original  being  placed  upon  a  drum  which  turns  round  under 
a  stylus,  or  its  equivalent,  while  the  stylus  gradually  travels 
along  from  end  to  end  after  the  manner  of  the  needle  of  a 
phonograph,  or  else  the  same  result  being  achieved  by  the 
drum  itself  having  an  endwise  movement  as  well  as  a  rotative 
one.  The  receiving  instrument  is  of  similar  form,  and  both 
must  start  together,  move  at  the  same  speed  and  indeed 
preserve  a  perfect  correspondence  with  each  other. 

If  the  distance  be  great  between  the  two  there  may  be 
difficulties  due  to  the  "  retardation  "  of  the  currents  passing 
between  them.  Electricity  does  not  pass  through  long 
wires,  particularly  if  they  be  under  the  sea,  with  anything 
like  the  quickness  which  we  are  apt  to  think.  Over  a  short 
line  and  under  favourable  circumstances  the  receipt  of  a 
telegraph  signal  at  the  farther  end  is  practically  instan- 
taneous, but  on  long  lines,  and  under  certain  conditions, 
that  is  far  from  being  the  case. 

Then  something  has  to  be  done  to  quicken  the  action 
of  the  current,  or  else  the  receiving  drum  must  be 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE     188 

made  to  lag  behind  the  sending  drum  by  the  requisite  amount. 
In  some  cases,  too,  the  transmitting  apparatus  loses  a  little 
time  in  sending  off  the  currents,  and  that,  too,  has  to  be 
allowed  for,  so  that,  all  things  considered,  the  reader  will  see 
that  the  successful  solution  of  this  problem  is  hedged  about 
with  many  subtle  difficulties  which  are  probably  only 
appreciated  by  those  who  are  well  acquainted  by  sad 
experience  with  the  little  vagaries  of  both  electricity  and 
mechanical  devices.  Neither  of  them  does  quite  what  we 
want  it  to  do  ;  each  suffers  from  little  faults,  which  in  the 
case  of  a  delicate  problem  like  this,  where  a  difference  of  a 
hundredth  of  a  second  would  be  fatal  to  success,  introduce 
difficulties  almost  insuperable. 

To  transmit  line  drawings,  Professor  Korn  uses  a  sending 
instrument  very  like  that  of  Caselli.  The  picture  is  placed, 
either  by  hand  or  photographically,  upon  a  sheet  of  copper 
foil,  which  is  fixed  round  the  rotating  cylinder,  the  lines 
being  formed  of  non-conducting  material.  The  foil  being 
electrified  and  the  stylus  connected  to  the  "  line  "  or  main 
wire,  currents  pass  to  the  farther  end  just  as  in  the  old 
apparatus. 

At  the  receiving  end  the  drum  is  covered  with  photo- 
graphic paper  and  enclosed  in  a  light-tight  box.  Through 
a  hole  in  this  box  a  fine  pencil  of  light  passes  from  a 
lamp,  suitable  lenses  being  used  to  ensure  that  the  pencil 
shall  have,  as  it  were,  a  very  fine  point,  producing  a  very 
small  spot  of  light  upon  the  paper.  If  the  light  remains 
quite  steady,  the  drum  meanwhile  rotating,  a  line  will  be 
drawn  by  it  upon  the  paper  which  will  be  visible  when 
the  latter  is  developed.  Since  the  drum  not  only  turns  upon 
its  axis,  but  also  moves  endwise  one  hundredth  of  an  inch 
at  every  revolution,  this  line  will  be  a  spiral,  the  turns  of 
which  will  IDC  one  hundredth  of  an  inch  apart.  Thus  the 
paper  will  be  blacked,  practically  uniformly,  all  over. 
Should  the  intensity  of  the  light  vary,  however,  the  line 
will  at  times  be  lighter  than  at  others,  while,  should  it 
be  cut  off  altogether  for  a  moment,  then  there  will  be  a 


184      HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

corresponding  gap  in  the  line,  and  it  is  easy  to  see  that  if 
these  lighter  parts  or  gaps  occur  in  the  correct  places  they  will 
form  a  picture.  In  other  words,  by  controlling  that  light 
we  can  build  up  a  picture  upon  the  paper.  The  question  is 
how  to  control  it. 

Professor  Korn  uses  a  form  of  the  Einthoven  galvanometer 
already  described.  Instead  of  the  silvered  fibre  generally 
employed  in  this  instrument,  a  silver  wire  is  fitted,  the 
movement  of  which  partly  or  entirely  cuts  off  the  pencil  of 
light. 

The  Korn  transmitter  for  photographs  is  quite  different, 
although  the  receiver  is  practically  the  same  as  what  has 
just  been  described.  The  basis  of  it  is  a  peculiar  power 
possessed  by  the  metal  selenium  when  in  a  certain  state. 
This,  like  all  metals,  is  a  conductor  of  electricity,  but  of 
course  offers  resistance  in  some  degree.  Now  the  special 
feature  of  selenium  is  that  its  resistance  is  reduced  if  light 
shine  upon  it.  Suppose,  then,  that  current  be  flowing 
through  a  mass  of  selenium  and  that  the  latter  be  suddenly 
illuminated  brightly,  the  resistance  will  at  once  fall  and  the 
current  increase.  On  the  other  hand,  should  the  light 
falling  upon  the  selenium  diminish,  its  resistance  will  increase 
and  the  current  flowing  through  it  will  decrease.  In  short, 
given  a  suitable  arrangement,  the  current  flowing  in  a  circuit 
of  which  a  selenium  "  cell  "  forms  a  part  will  increase  or 
decrease  with  the  increase  or  decrease  in  the  light  falling 
upon  the  cell. 

A  while  ago  the  papers  were  telling  striking  stories  of  a 
way  by  which  blind  people,  so  it  was  said,  were  to  be  recom- 
pensed for  the  loss  of  their  sight — a  new  sense,  as  it  were, 
was  to  be  given  them  by  which  they  could  "  hear  "  light, 
even  if  they  could  not  see  it.  All  this  had  reference  to  this 
curious  property  of  selenium,  it  being,  of  course,  an  un- 
doubted fact  that  it  will  vary  an  electric  current  in  accord- 
ance with  the  variations  in  the  light,  and  if  that  current  be 
led  through  a  telephone  receiver  a  man,  by  holding  that  to 
his  ear,  could,  in  a  sense,  hear  the  variations  in  the  light. 


THE  TELEWRITER 

This  remarkable   instrument   transmits   actual  writing   and   drawings,   the 
receiving  pen  copying  precisely  the  movements  of  the  sending  pen 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE      185 

In  the  Korn  transmitter  for  photographs  selenium  is  em- 
ployed as  follows  : — A  transparent  photograph  is  made,  on 
a  celluloid  or  gelatine  film,  and  this  is  fixed  upon  a  glass 
cylinder  mounted  as  already  described.  A  pencil  of  light 
falls  upon  this  in  much  the  same  way  as  in  the  case  of  the 
receiver  just  described,  and,  as  the  cylinder  revolves,  describes 
a  fine  spiral  line  all  round  and  round  it. 

Moreover,  the  light  passes  right  through  the  photograph 
and  falls  upon  a  mirror  inside,  off  which  it  is  reflected  on  to  a 
selenium  cell.  At  every  moment,  then,  the  light  is  falling 
upon  some  small  part  of  the  photograph,  and  the  amount  of 
it  which  gets  through  and  ultimately  reaches  the  selenium 
depends  upon  the  density  of  that  part. 

Current,  meanwhile,  is  flowing  from  a  battery  through  the 
selenium,  and  thence  over  the  main  wire  to  the  distant  station. 
As  the  light  pencil  traces  its  spiral  path  over  the  rolled  up 
photograph  every  variation  in  the  density  of  the  picture  is 
reproduced  as  a  variation  in  the  current  through  the  selenium. 
This,  at  the  remote  end,  operates  the  Einthoven  galvanometer, 
the  movements  of  which  vary  the  shade  of  the  spiral  line 
being  drawn  upon  the  photographic  paper. 

This  process  takes  place  with  remarkable  celerity,  so  that 
in  a  few  minutes  the  innumerable  variations  constituting  a 
complete  photograph  can  be  transmitted  and  faithfully 
recorded  at  the  distant  end  of  the  wire. 

But  perhaps  the  most  successful  of  these  methods  is  that 
known  as  the  t electr ograph .  It  is  surprisingly  like  the  scheme 
of  Caselli  in  principle,  and  forms  another  example  of  the  fact 
that  good  ideas  often  fail  through  lack  of  the  proper  means 
to  carry  them  out.  Mr  Thorne-Baker,  the  inventor  of  the 
telectrograph,  has  had  at  his  disposal  accumulated  stores  of 
knowledge  and  skill  which  did  not  exist  in  Caselli's  time. 
Consequently  the  former  has  made  a  brilliant  success  where 
his  predecessor  produced  only  an  interesting  but  somewhat 
ineffective  attempt. 

Reference  has  been  made  already  to  the  half-tone  blocks 
wherein  a  host  of  small  dots  of  varying  sizes  make  up  a 


186      HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

picture.  Now  instead  of  parallel  rows  of  dots  parallel  lines 
of  varying  thickness  will  give  very  much  the  same  result. 
The  former  are  made  by  photographing  the  picture  through 
a  sheet  of  glass  ruled  with  two  sets  of  lines  at  right  angles  to 
each  other.  The  latter  can  be  made  by  using  a  screen  with 
lines  one  way  only  instead  of  two  ways.  It  is  therefore  quite 
easy  for  a  blockmaker  to  produce  a  "  process  block  "  wherein 
lines  are  used  instead  of  dots.  For  this  particular  purpose, 
however,  it  is  not  an  ordinary  block  that  is  needed,  although 
it  is  in  essentials  very  similar.  The  picture  to  be  transmitted 
is  photographed  through  a  screen  as  if  a  half-tone  block  were 
to  be  made.  The  negative  so  obtained  is  then  printed  by 
the  gum  process  on  to  a  sheet  of  soft  lead  and,  after  washing, 
the  picture  remains  upon  the  lead  in  the  form  of  lines  of  in- 
soluble gum  on  a  background  of  bare  lead.  A  squeeze  in  a 
press  drives  the  gum  into  the  lead,  and  so  gives  the  whole 
sheet  a  smooth  surface  over  which  a  stylus  will  ride  easily, 
but  which  is,  nevertheless,  made  up  of  conductive  parts  and 
non-conductive  parts,  the  latter  forming  the  picture. 

The  lead  sheet  is  then  put  upon  a  revolving  cylinder  and 
turned  under  a  moving  stylus  in  the  manner  with  which  we 
are  now  familiar.  The  sheet  is  placed  with  the  lines  length- 
wise of  the  cylinder  so  that  current  passes  to  the  stylus  except 
as  it  passes  over  the  breadth  of  the  lines,  and  so  similar  lines 
are  built  up  at  the  distant  end. 

The  receiving  mechanism  is  of  the  electro-chemical  type 
which  Caselli  used.  The  current  passes  from  the  receiving 
stylus  to  the  paper,  and  there  makes  its  mark  in  a  way  that 
will  be  understood  from  the  description  of  the  earlier 
apparatus. 

The  supreme  advantage  of  this  method  of  working,  over 
that  of  Professor  Korn,  is  that  the  operator  can  see  what  he  is 
doing.  To  obtain  good  results,  a  number  of  electrical  adjust- 
ments have  to  be  made,  and  whether  he  has  got  them  right 
or  wrong  can  be  seen  as  soon  as  the  picture  begins  to  grow 
upon  the  receiving  paper.  If  a  little  readjustment  be  needed 
the  operator  sees  it  and  can  set  things  right  before  the  really 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE    187 

important  part  of  the  picture  begins  to  appear,  whereas  with 
the  Korn  apparatus  he  does  not  know  what  is  happening  at 
all,  since  he  can  see  nothing  until  the  picture  is  finished  and 
the  photographic  paper  has  been  developed. 

It  will  be  apparent,  too,  to  anyone  who  has  carefully  con- 
sidered the  wireless  telegraphy  chapters,  that  it  ought  to  be 
possible  to  make  the  sending  stylus  or  its  equivalent  control 
a  wireless  transmitter  and  a  wireless  receiver  to  operate  the 
receiving  stylus,  so  as  to  be  able  to  send  pictures  by  "  wire- 
less." Experiments  to  this  end  have  been  made  with  some 
measure  of  success,  and  sooner  or  later  we  are  almost  sure 
to  hear  that  the  difficulties,  which  are  by  no  means  small, 
have  been  overcome. 

But  we  cannot  conclude  this  chapter  without  a  fuller 
reference  to  that  marvellous  invention,  the  telewriter. 

In  this  a  man  makes  a  sketch  with  a  pen  on  a  piece  of 
paper,  or  maybe  he  writes  a  message,  and  simultaneously  a 
pen,  hundreds  of  miles  away  if  need  be,  does  precisely  the 
same  thing.  The  receiving  instrument  draws  the  sketch 
line  by  line,  or  it  transcribes  the  message  in  the  actual  hand- 
writing of  the  sender.  A  little  touch,  almost  weird  in  its 
naturalness,  is  that  every  now  and  then  the  receiving  pen 
leaves  the  paper  and  dips  itself  into  a  bottle  of  ink,  after 
which  it  resumes  its  work  at  the  very  spot  where  it  left  off. 

Now  how  the  complicated  lines  and  curves,  the  strokes  and 
dots  which  make  up  a  written  language,  even  the  little  shakes 
and  defects  which  give  each  man's  writing  a  personality  of  its 
own,  how  all  these  can  be  sent  over  a  wire  is  at  first  sight 
very  difficult  to  understand.  The  inventor  of  this  apparatus 
has  discovered  an  extremely  simple  way  of  doing  it. 

But  even  he  does  not  attempt  to  do  it  with  one  wire,  it 
should  be  said,  for  he  uses  two.  This  is  no  drawback  when, 
as  is  often  the  case,  it  is  used  in  conjunction  with  a  telephone, 
for  the  latter,  to  be  effective,  also  requires  two  wires.  Years 
ago  single  wires  were  employed  for  telephones  as  for  tele- 
graphs, the  circuit  being  completed  through  the  earth.  But 
the  difficulty  arose  that  every  wire  through  which  currents 


188    HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

flow  is  apt  to  induce  currents  in  neighbouring  wires — the 
induction  coil  is  based  upon  that  fact — and  so  messages  in 
one  wire  were  overheard  on  others,  or,  what  was  perhaps  more 
annoying  still,  the  dots  and  dashes  passing  in  a  telegraph  wire 
would  produce  loud  noises  in  a  telephone  wire  that  happened 
to  be  near.  The  use  of  two  wires,  however,  entirely  removes 
that  trouble,  for  the  neighbouring  current  then  induces  two 
currents  instead  of  one,  one  in  each,  and  it  so  happens  that 
these  are  opposed  to  each  other,  so  that  they  neutralise  each 
other.  So  every  telephone  wire  now  is  double  and  therefore 
is  ready,  as  it  were,  to  have  the  telewriter  fitted  to  it. 

But  even  with  two  wires  the  difficulty  seems  insuperable 
until  we  remember  that  the  most  complex  of  curves  can  be 
resolved  into  two  simple  movements. 

The  sending  pen,  with  which  the  original  writing  or  draw- 
ing is  done,  is  attached  to  the  junction  of  two  light  rods. 
The  farther  end  of  each  rod  is  attached  to  the  end  of  a  light 
crank  fixed  so  that  it  can  rotate  or  oscillate,  after  the  manner 
of  cranks,  in  the  plane  of  the  desk  upon  which  the  paper  lies. 
All  the  joints  mentioned  are  of  the  hinge  nature,  so  that  as  the 
pen  is  moved  about  the  rods  turn,  more  or  less,  one  way  or 
the  other,  the  two  cranks.  This  simple  mechanism,  it  will 
be  observed,  carries  out  very  effectively  the  principle  just 
mentioned,  for  it  resolves  the  motion  of  the  pen,  no  matter 
how  complicated  it  may  be,  into  a  simple  rotating  motion  of 
the  two  cranks. 

So  the  cranks  turn  this  way  or  that  as  the  draughtsman 
makes  his  picture,  and  it  is  very  easy  to  arrange  that  their 
movement  shall  vary  the  strength  of  two  electric  currents, 
whereby  we  obtain  electric  currents  varying  in  accordance 
with  the  movement  of  the  cranks. 

This  is  done  by  making  each  crank  operate  a  variable 
resistance  or  rheostat.  When  in  its  extreme  position  on  one 
side  the  crank  permits  current  to  flow  freely,  but  as  it  moves 
over  to  the  other  extreme  position  the  resistance  in  the 
path  of  the  current  is  increased.  Such  an  arrangement  is  a 
common  feature  in  electrical  apparatus. 


HOW  PICTURES  CAN  BE  SENT  BY  WIRE     189 

So  current  from  a  battery  flows  to  the  two  wires  leading 
to  the  distant  station,  each  passing  through  the  rheostat 
connected  to  one  of  the  cranks.  We  may  think  of  the 
rheostats  as  taps  which  can  be  turned  on  or  off  by  the  action 
of  the  cranks.  Let  us  imagine  that  crank  a  is  in  the  position 
when  the  current  flows  freely — when  the  electrical  "  tap  "  is 
fully  open  ;  then  a  strong  current  will  flow  along  wire  a, 


FIG.  15.— A  Message  received  by  Telewriter. 

returning  to  the  sending  battery  via  the  earth.  As  that  crank 
is  moved  the  current  will  gradually  be  reduced,  until,  if  it 
be  moved  right  over  to  the  other  extreme,  the  current  will 
be  at  its  feeblest. 

Arrived  at  the  other  end,  this  current  passes  to  a  device 
which  we  may  describe  simply  as  a  magnet  so  arranged  that 
its  action  pulls  round  a  crank  against  the  restraining  action 
of  a  spring. 

Now  the  stronger  the  current  the  more  does  that  magnet 
pull  and  the  farther  does  the  receiving  crank  turn.  The 
sending  crank  varies  the  resistance,  the  resistance  varies 
the  current,  the  current  varies  the  strength  of  the  receiving 


190     HOW  PICTURES  CAN  BE  SENT  BY  WIRE 

magnet,  and  the  magnet  varies  the  position  of  the  receiving 
crank.  Properly  adjusted,  then,  the  motion  of  the  crank 
at  the  one  end  is  communicated  through  that  long  chain  of 
causes  and  effects,  until  at  last  it  is  repeated  exactly  by 
the  movement  of  the  crank  at  the  other  end. 

The  same  thing  occurs  simultaneously  over  each  of  the 
two  wires,  crank  a  at  the  sending  end  communicating  over 
wire  a  to  crank  a  at  the  other  end,  while  crank  b  communi- 
cates its  motion  over  wire  b  to  the  other  crank  b.  Each 
sending  crank  is  closely  imitated  in  its  every  action  by  the 
corresponding  one  at  the  distant  station. 

The  two  receiving  cranks  are  connected  by  light  rods  to 
the  receiving  pen  in  precisely  the  same  way  that  the  sending 
pen  is  connected.  Consequently,  not  only  are  the  separate 
movements  of  the  two  cranks  repeated  at  the  remote  station 
but  the  complex  movements  of  the  sending  pen,  which 
gave  rise  to  the  actions  of  the  cranks,  are  also  conveyed  to, 
and  repeated  by,  the  recording  pen.  The  movements  of 
the  first  pen  are  resolved  into  rotating  motions  by  the  two 
cranks,  these  are  transferred  to  the  other  cranks,  and  their 
movements  are  in  turn  converted  back  into  the  written 
curves. 

Thus  as  the  pen  in  the  artist's  hand  draws  his  sketch,  so 
does  the  automatic  hand  at  the  other  place,  it  may  be  at  a 
great  distance,  repeat  faithfully  his  work,  and  the  sketch 
grows  line  by  line  simultaneously  at  both  ends. 

There  is  not  space  here  to  detail  how,  by  another  current 
superposed  upon  those  referred  to  already,  the  receiving-pen 
is  made  to  dip  itself  periodically  into  the  inkwell  at  the  will 
of  the  sender.  By  a  cunning  use  of  alternating  current  this 
is  done  without  in  any  way  interfering  with  the  action  of 
the  cranks  as  described  above. 

But  of  course  there  is  a  severe  limitation  to  the  usefulness 
of  this  machine,  inasmuch  as  the  drawing  has  to  be  made 
at  the  time  of  transmission,  and  it  can  only  be  "  put  on  the 
wire  "  by  the  hand  of  the  artist  himself. 


CHAPTER  XIV 

A  WONDERFUL  EXAMPLE   OF  SCIENCE  AND   SKILL 

IN  the  preceding  chapter  reference  was  made  to  the  fact 
that  for  the  successful  sending  of  pictures  "  by  wire  " 
one  thing  was  necessary  above  all  others.  That  one 
thing  consists  in  making  two  machines,  perhaps  hundreds  of 
miles  apart,  start  working  together,  stop  together  and,  when 
working,  turn  at  exactly  the  same  speed.  Let  the  reader 
just  picture  the  problem  to  himself,  and  ask  himself  how 
such  an  arrangement  can  be  possible.  Let  him  think  of  a 
town  two  hundred  miles  away  and  then  meditate  on  the 
possibility  of  making  a  machine  working  in  his  own  room 
and  another  in  that  distant  town  maintain  perfect  unanimity 
in  their  movements.  The  result  of  such  reflection  will 
probably  be  the  assertion  that  such  a  thing  is  beyond  the 
bounds  of  possibility.  Then  he  will  find  the  following 
description  of  how  it  is  done  extremely  interesting. 

In  the  first  place  it  must  be  understood  that  each  machine 
is  driven  by  an  electric  motor.  The  motors  are  designed 
to  run  at  3000  revolutions  per  minute,  and  they  drive  the 
cylinders  of  the  machines  through  gearing  so  arranged  that 
the  latter  turn  at  50  revolutions  per  minute. 

Now  of  all  machines  perhaps  the  most  docile  and  easily 
managed  is  the  direct-current  electric  motor.  Each  such 
machine  is  made  with  a  view  to  its  working  at  a  certain  speed, 
but  that  can  be  varied  within  certain  limits,  by  simply 
varying  the  force  of  the  current  which  drives  it.  And  that 
force  can  be  very  easily  varied  by  the  use  of  an  instrument 
called  a  "rheostat"  or  variable  resistance.  We  are  all 
familiar  with  the  way  in  which  the  engine-driver  regulates 
the  speed  of  a  locomotive,  by  means  of  a  valve  in  the  steam- 
191 


192  A  WONDERFUL  EXAMPLE  OF 

pipe.  The  opening  and  closing,  more  or  less,  of  the  valve 
enables  the  speed  to  be  changed  at  will  and  adjusted  to  a 
nicety.  The  rheostat  is  to  the  electric  current  what  the 
valve  is  to  the  steam ;  it  can  be  opened  and  closed,  more  or 
less,  as  necessary.  By  it  the  current  driving  the  motor  can 
be  made  stronger  or  weaker,  and  as  that  change  is  made 
so  does  the  speed  of  the  motor  change  accordingly.  Thus 
we  see  that  there  is  at  hand  the  means  of  setting  a  motor  to 
work  at  any  desired  speed. 

The  difficulty,  however,  is  to  tell  when  the  desired  speed 
has  been  attained.  One  can  count  the  revolutions  of  a 
machine  at  two  or  three  revolutions  per  minute  with  a  certain 
amount  of  accuracy,  but  fifty  revolutions  per  minute  are 
more  than  one  could  count  correctly.  Still  less  could  we 
count  the  3000  revolutions  every  minute  of  the  motors. 
Thus,  even  if  we  had  the  two  motors  side  by  side,  we  should 
have  extreme  difficulty  in  making  them  work  at  the  same 
speed  exactly.  One  might  be  doing  3000  while  the  other 
did  2990  or  3010  and  we  should  be  none  the  wiser.  And 
when  we  separate  the  two  by  a  distance  of  many  miles, 
the  task  of  synchronising  them  is  even  worse. 

But  fortunately  there  is  a  simple  contrivance  by  which 
we  can  tell  very  accurately  the  speed  of  a  motor.  The  reader 
has  already  been  familiarised,  in  previous  chapters,  with  the 
difference  between  direct  or  continuous  electric  currents  and 
alternating  ones.  It  is  the  continuous  sort  which  is  used  to 
drive  these  motors,  but  a  slight  addition  to  the  machine  will 
make  it  so  that  while  direct  current  is  put  in,  to  drive  it, 
alternating  current  can  be  drawn  out  of  it.  Two  little 
insulated  metal  rings  are  fitted  on  to  the  spindle  of  the 
machine,  and  these  are  connected  in  certain  ways  to  the 
wires  of  the  motor  ;  then  against  these  rings,  as  they  turn, 
there  rub  two  little  metal  arms,  called,  because  of  their 
sweeping  action,  brushes ;  and  from  these  brushes  we  can 
draw  the  alternating  current. 

For  our  present  purpose  the  importance  of  this  lies  in  the 
fact  that  the  rate  at  which  that  current  will  alternate 


SCIENCE  AND  SKILL  198 

depends  upon  the  speed  of  the  motor.  As  the  motor  increases 
or  decreases  in  speed,  so  will  the  rate  of  alternation  increase 
or  decrease.  So  that  if  we  can  measure  the  rate  at  which 
the  current  drawn  from  the  motor  is  alternating,  we  shall 
know  from  that  the  rate  at  which  the  machine  is  working. 

This  we  can  do  by  the  aid  of  a  "  frequency  meter."  The 
working  of  this  is  based  upon  the  acting  of  a  tuning-fork. 
Everyone  knows  that  a  given  tuning-fork  always  gives  out 
the  same  note.  The  note  depends  upon  the  rate  at  which 
the  fork  vibrates,  and  the  reason  that  one  fork  always  gives 
the  same  note  is  because  it  always  vibrates  at  the  same 
rate.  That  rate,  in  turn,  depends  upon  its  length.  If  one 
were  to  file  a  little  off  the  end  of  a  tuning-fork,  its  note  would 
be  raised,  because  its  rate  of  vibration  would  become  faster. 
Similarly,  lengthening  the  fork  would  result  in  a  lower  note 
being  given.  Thus,  a  tuning-fork,  or  any  bar  of  steel  held 
by  one  end,  and  free  to  vibrate  at  the  other,  gives  us  a 
standard  of  speed  which  is  very  reliable.  And  it  so  happens 
that  we  can  easily  use  a  set  of  such  forks  to  test  the  rate 
of  alternation  of  an  alternating  current. 

Generally  speaking,  alternating  current  is  no  use  for  energis- 
ing a  magnet.  The  chief  reason  for  that  is  that  the  current 
tends  to  get  choked  up,  as  it  were,  in  the  coil.  Alternating 
current  traverses  a  coil  very  reluctantly  indeed.  It  is, 
however,  possible  to  make  an  electric  magnet  of  special 
design  which  will  work  sufficiently  well  with  alternating 
current  to  answer  our  present  purpose.  And  it  will  be  clear 
that  just  as  the  alternating  current  itself  consists  of  a  series 
of  short  currents,  so  the  force  of  the  magnet  will  be  inter- 
mittent ;  it  will  give  not  a  steady  pull,  as  is  usually  the  case 
with  magnets,  but  a  succession  of  little  tugs.  There  will, 
in  fact,  be  one  tug  for  every  alternation  of  the  current. 

A  simple  form  of  motor  fitted  up  as  just  described,  and 
rotating  at  3000  revolutions  per  minute,  would  give  out 
100  alternations  per  second.  If,  then,  such  current  were 
employed  to  energise  a  magnet,  that  magnet  would  give 
100  tugs  per  second. 

N 


194  A  WONDERFUL  EXAMPLE  OF 

So  a  small  steel  bar  of  the  right  length  to  give  100  vibra- 
tions per  second  can  be  fixed  with  its  free  end  nearly 
touching  such  a  magnet,  and  when  the  current  is  turned  on 
it  will  very  soon  be  vibrating  vigorously.  For  the  tugs  of 
the  magnet  will  agree  with  the  natural  rate  of  vibration  of 
the  bar.  And  just  as  the  two  pendulums  described  in 
Chapter  XII.  responded  readily  to  each  other,  so  the  bar 
responds  readily  to  the  pulls  of  the  magnet.  But  increase 
or  decrease  the  rate  of  alternation  ever  so  slightly,  and  that 
sympathy  between  magnet  and  bar  is  destroyed.  The  bar 
will  not  then  respond.  It  will  only  answer  when  the  pulls 
of  the  magnet  and  the  natural  rate  of  vibration  of  the  bar 
exactly  correspond. 

So  it  is  usual  to  place  five  or  six  such  bars  with  their  ends 
near  the  one  magnet.  The  lengths  of  the  bars  vary  slightly, 
so  that  the  rates  of  vibration  are,  say,  98,  99,  100, 101, 102 
respectively. 

Let  us,  in  imagination,  adjust  the  speed  of  a  sup- 
posititious motor  until  we  get  that  which  corresponds  to 

100  alternations. 

We  switch  on  the  current  and  at  first,  possibly,  we  get  no 
response  from  any  of  the  vibrating  bars.  Just  a  touch  to 
the  handle  of  the  rheostat  and  we  notice  that  bar  102  shows 
signs  of  life.  We  see  then  that  our  first  speed  was  much 
too  fast,  and  that  reducing  it  has  brought  it  down  to  102, 
which  is  still  a  little  too  fast.  Just  a  little  more  movement 
of  the  handle,  and  102  begins  to  relapse  into  quiet,  while 

101  shows  animation.    A  little  more  movement  and  101 
gives  place  to  100,  and  then  we  know  that  our  motor  is 
working  at  the  desired  speed.    If  our  motor  had  been  too 
slow  to  commence  with,  it  would  have  been  98  which  first 
got  into  action,  but  the  method  of  adjustment  would  have 
been  precisely  the  same. 

And  thus  we  see  the  whole  scheme.  We  regulate  the 
speed  by  the  rheostat,  and  meanwhile  that  tell-tale  stream 
of  alternating  current  comes  flowing  out  of  the  motor  to 
indicate  to  us  what  the  speed  is,  while  the  "  frequency 


SCIENCE  AND  SKILL  195 

meter,"  with  its  various  vibrating  bars,  interprets  to  us  the 
message  which  the  alternating  current  brings  to  us.  So  by 
watching  the  meter  we  know  when  we  have  got  the  speed 
that  we  desire. 

But  even  that  is  only  half  the  battle.  We  have  seen  how 
to  make  a  machine  turn  at  any  desired  speed,  and  so  we  can 
adjust  any  two,  so  that  they  revolve  at  the  same  speed,  but 
we  have  not  seen  how  to  start  and  stop  the  two  machines 
at  the  same  time. 

First  of  all,  it  must  be  understood  that  in  the  case  of  the 
receiving  machine  there  is  a  friction  clutch,  as  it  is  termed, 
between  the  motor  and  the  cylinder  which  it  is  driving. 
That  means  that  while,  under  ordinary  circumstances,  the 
motor  drives  the  cylinder  round,  we  can,  if  we  like,  hold  the 
latter  still  without  stopping  the  motor.  When  we  do  so, 
the  connection  between  the  two  simply  slips. 

So  if  we  fit  a  catch  on  the  cylinder  which  is  capable  of 
holding  it  from  rotating,  we  can  still  start  the  motor,  and 
the  latter  will  work.  Then,  the  moment  the  catch  is  released 
the  cylinder  will  begin  to  turn  too.  The  commonest  form 
of  "  friction  drive  "  is  the  flat  leather  belt  upon  two  pulleys, 
which  everyone  has  seen  at  some  time  or  other  in  a  factory. 
And  it  will  be  quite  easy  to  conceive  how,  if  one  of  the 
driven  machines  were  to  stick,  the  belt  might  simply  slip 
upon  one  of  the  pulleys,  yet,  as  soon  as  the  machine  became 
free  again,  it  would  rotate  just  as  it  did  before.  It  is  just 
the  same  with  what  we  are  considering.  The  motor  works 
continuously  at  its  proper  speed,  but  the  cylinder  can  be 
stopped  when  desired  by  the  catch. 

Combined  with  the  catch  is  an  electro-magnet,  and  through 
its  coils  there  flows  the  current  of  electricity  which  is  engaged 
in  printing  the  picture  on  the  cylinder.  If  a  magnet  be 
arranged  to  attract  another  magnet,  it  will  do  so  only  when 
the  energising  current  flows  one  way.  When  it  flows  the 
other  way,  it  does  not  attract.  Therefore  it  is  easy  to  arrange 
matters  so  that  the  printing  current,  though  passing  through 
the  coil  of  the  magnet,  shall  not  pull  open  the  catch.  But  if 


196  A  WONDERFUL  EXAMPLE  OF 

that  current  be  reversed  in  direction  for  a  moment  the 
magnet  gives  a  pull,  open  flies  the  catch,  and  away  goes 
the  cylinder  upon  its  revolution. 

Thus,  we  see,  all  that  is  necessary  to  start  the  receiving 
cylinder  is  to  reverse  the  current  for  a  moment. 

And  now  let  us  turn  our  attention  to  the  sending  machine. 
Upon  its  cylinder  there  is  an  arrangement  which  automatic- 
ally reverses  the  current  flowing  to  the  main  wire  once  in 
every  revolution.  Normally  the  current  flows  to  the  wire 
as  described  in  the  last  chapter,  carrying  by  means  of  its 
variations  the  details  of  the  picture  for  reproduction  by  the 
receiving  machine  at  the  other  end.  But  for  an  instant  once 
in  every  revolution  that  current  is  interrupted  and  a  current 
sent  in  the  opposite  direction  instead.  This  the  sending 
machine  does  of  itself,  quite  automatically. 

And  now  the  reader  knows  of  all  the  apparatus ;  it 
remains  only  to  see  how  the  different  parts  work  in 
combination. 

Standing  by  the  sending  machine  we  first  of  all  turn  on  the 
current,  which  goes  coursing  along  the  wire  to  the  distant 
station.  Then  we  set  the  motor  to  work  and  the  cylinder 
begins  to  rotate.  Before  it  has  completed  a  single  revolu- 
tion the  "  reverser  "  is  operated,  and  just  for  a  moment  the 
reverse  current  goes  to  the  wire.  On  arrival  at  the  other 
end  that  lifts  the  catch  and  the  receiving  cylinder  starts. 
That  first  partial  revolution  of  the  sending  cylinder  counts 
for  nothing.  Real  business  begins  when  the  reverser  first 
acts,  and  that  is  the  moment  when  the  receiving  cylinder 
also  begins  to  move.  Similarly,  when  the  sending  cylinder 
stops  it  sends  no  more  reversed  currents,  and  so  the  receiving 
cylinder  is  caught  by  the  catch  and  not  released. 

So  starting  and  stopping  are  quite  automatic.  The  same 
arrangement  enables  a  continual  readjustment  of  the 
relative  speed  of  the  two  cylinders  to  take  place.  With  all 
the  best  devices,  the  tuning-forks  and  the  rest,  it  is  still 
impossible  to  attain  perfect  unanimity,  but  the  variation 
in  a  single  revolution  cannot  be  enough  to  matter ;  it  is 


SCIENCE  AND  SKILL  197 

only  when  the  error  in  one  revolution  goes  on  multiplying 
itself  that  serious  difference  might  arise,  and  that  is  prevented 
in  the  following  beautifully  simple  way. 

The  motor  which  drives  the  receiving  drum  is  so  regulated 
that  it  travels  slightly  faster  than  does  the  other.  Thus  the 
receiving  cylinder  completes  every  revolution  slightly  in 
advance  of  the  other,  and  consequently  it  is  stopped  and 
held  by  the  catch  every  time.  The  catch  retains  it,  of 
course,  until  the  reverse  current  arrives  and  releases  it. 
Thus  not  only  does  the  sending  cylinder  start  the  other 
when  the  operations  first  commence,  but  it  does  so  every 
revolution.  Every  revolution,  therefore,  the  two  cylinders 
start  together. 

So  the  two  cylinders  are  set,  according  to  the  frequency 
meter,  at  as  nearly  as  possible  exactly  the  correct  speeds,  and 
the  action  of  the  reverser,  the  reverse  current  and  the  catch, 
ensures  quite  automatically  that  at  the  commencement  of 
every  revolution  there  shall  be  perfect  agreement  between 
the  two.  No  accumulation  of  errors  can  possibly  occur,  and 
the  problem,  though  apparently  so  difficult,  if  not  insuper- 
able, at  first  sight,  is  surmounted. 


CHAPTER  XV 

SCIENTIFIC   TESTING  AND  MEASURING 

SCIENCE,  whether  it  be  of  the  pure  variety,  that 
which  is  pursued  for  its  own  sake — for  the  mere 
greed  for  knowledge — or  applied  science,  the  purpose 
of  which  is  to  assist  manufacture,  is  based  entirely  upon 
accurate  testing  and  measuring.  It  is  only  by  discovering 
and  investigating  small  differences  in  size,  weight  or  strength 
that  some  of  the  most  important  facts  can  be  brought  to 
light.  There  are  some  problems,  too,  that  defy  theory, 
since  they  are  too  complicated ;  they  involve  too  many 
theories  all  at  once,  and  such  can  only  be  solved  by  accurate 
tests.  And  all  these  necessitate  the  use  of  very  ingenious 
and  often  costly  devices. 

Electrical  measuring  instruments  were  of  sufficient  im- 
portance and  interest  to  warrant  a  chapter  of  their  own,  but 
there  are  many  others  of  great  value,  and  not  without 
interest  to  the  general  reader. 

For  example,  some  years  ago  there  was  a  collision  in  the 
Solent,  just  off  Cowes,  between  the  cruiser  Hawke  and  the 
giant  liner  Olympic.  The  cause  of  this  was  a  subject  of 
dispute  and  of  litigation ;  the  theorists  theorised ;  some 
reached  the  conclusion  that  the  Hawke  was  to  blame,  and 
others  the  Olympic ;  and  where  doctors  disagree  who  shall 
decide  ?  It  was  wisely  decreed  that  tests  should  be  made 
to  settle  the  question. 

The  main  point  was  this.  The  officers  of  the  Hawke, 
by  far  the  smaller  vessel,  averred  that  they  were  drawn  out 
of  their  course  by  suction  caused  by  the  movement  of  so 
large  a  ship  as  the  Olympic  in  the  comparatively  narrow 
and  shallow  waters  of  the  Solent ;  in  other  words,  that  the 

198 


SCIENTIFIC  TESTING  AND  MEASURING      199 

Olympic  in  moving  through  the  water  caused  a  swirling, 
eddying  motion  in  the  water,  tending  to  draw  a  lighter 
vessel  towards  itself.  And  that  is  just  one  of  those  problems 
with  which  theory  is  unable  to  deal.  So  it  was  transferred 
to  the  National  Physical  Laboratory  at  Teddington,  near 
London,  for  investigation  by  experiment. 

At  this  institution,  which  is  a  semi-national  one,  there  is 
a  tank  constructed  for  purposes  such  as  this.  The  word 
tank  leads  us  to  underestimate  its  size  somewhat,  for  it  is 
494  feet  long  and  30  feet  wide.  It  is  solidly  constructed 
of  concrete,  with  a  miniature  set  of  docks  at  one  end,  and 
a  sloping  beach  at  the  other. 

On  either  side  are  rails  upon  which  run  trollys  which 
support  the  ends  of  a  bridge  which  spans  the  whole.  This 
bridge  can  be  propelled  along,  by  means  of  electric  motors 
operating  the  wheels  of  the  trollys,  from  one  end  of  the 
tank  to  the  other,  at  any  desired  speed,  within,  of  course, 
reasonable  limits,  and  from  it  may  be  towed  any  model 
which  it  is  desired  to  test. 

The  models  used  are  usually  made  of  wax,  by  means  of  a 
machine  specially  designed  for  the  purpose.  It  should  be 
explained  that  the  plans  of  a  ship  consist  of  a  series  of  curves, 
each  of  which  represents  the  contour  of  the  vessel  at  one 
particular  height.  For  example,  if  you  can  imagine  a  ship 
cut  horizontally  into  slices  of  uniform  thickness,  then  each 
slice  could  be  shown  on  the  drawing  (the  "  shear  plan,"  as 
it  is  termed)  by  a  curved  line.  Near  the  keel  the  lines 
would,  of  course,  be  almost  straight,  but  they  would  bulge 
more  and  more  as  they  occur  higher  up.  And  what  this 
machine  is  required  to  do  is  to  make,  quickly  and  economic- 
ally, a  wax  model  which  shall  be  an  exact  reproduction,  on  a 
small  scale,  of  the  vessel  under  discussion.  It  may  be — it 
most  often  is — a  ship  as  yet  unbuilt,  the  behaviour  of  which 
it  is  desired  to  test.  Or  it  may  be  an  existing  vessel,  as  it 
was  in  the  case  mentioned  just  now.  However  that  may 
be,  the  model  is  made  from  the  drawings. 

A  block  of  wax  rests  upon  a  table,  while  the  drawing  is 


200       SCIENTIFIC  TESTING  AND  MEASURING 

spread  upon  a  board  near  by.  A  pointer  is  moved  by  hand 
along  one  of  the  lines,  and  its  movement  is  repeated  by  a 
rapidly  revolving  cutter  which  cuts  away  the  wax  to  a 
similar  curve.  By  suitable  adjustments  the  cutter  can  be 
made  to  magnify  or  reduce  the  size,  so  as  to  produce  any 
desired  scale.  Thus  every  line  is  gone  over  and  a  similar 
curve  cut  in  the  wax  at  the  correct  height.  Of  course 
this  only  produces  a  lump  of  wax  shaped  in  steps,  as  it  were, 
but  it  is  then  quite  easy  to  trim  it  down  by  hand,  so  as  to 
produce  a  smooth  model  of  the  ship,  perfectly  accurate  in  its 
shape,  and  a  copy  on  a  small  scale  of  the  vessel  portrayed 
on  the  drawing. 

It  can  also  be  hollowed  out,  ballasted  with  weights 
inside,  and  so  made  to  sink  to  any  desired  level,  thereby 
representing  the  vessel  when  fully  loaded,  half  loaded  and 
so  on.  All  sorts  of  unequal  loading  can  be  produced  if 
needed,  indeed  every  condition  of  the  real  ship  can  be 
imitated  in  the  model. 

It  can  then  be  towed  to  and  fro  in  the  tank  by  the  travel- 
ling carriage  described  above.  The  speed  of  towing  can  be 
varied  by  changing  the  speed  of  the  motors  which  drive  it. 
The  force  needed  to  pull  the  model  through  the  water  is 
measured  by  means  of  a  dynamometer  which  registers  the 
pull  on  the  towing  apparatus. 

A  matter  very  often  needing  investigation  is  the  shape  and 
size  of  the  wave  thrown  up  by  the  bow  of  the  vessel,  and 
of  that  left  behind  her,  known  as  the  "  bow  wave  "  and  the 
"  stern  wave  "  respectively.  These  waves  represent  wasted 
energy,  for  they  are  no  use  and  are  produced  actually  by 
the  power  of  the  engines  of  the  ship  as  they  drive  her  along. 
The  ideal  ship  would  cause  no  waves,  but  since  that  is  a 
degree  of  perfection  impossible  even  to  hope  for,  the  ship- 
builder has  to  content  himself  by  so  designing  his  ships  that 
these  waves  shall  be  as  small  as  possible. 

The  waves  are  recorded  photographically,  in  some  cases 
by  the  kinematograph. 

Some  of  the  large  shipbuilders  have  their  own  tanks,  and 


SCIENTIFIC  TESTING  AND  MEASURING      201 

so  have  the  naval  authorities  of  the  great  naval  Powers. 
The  one  at  Teddington  was  established  through  the  munifi- 
cence of  a  famous  British  shipbuilder,  Mr  Yarrow,  who  not 
only  defrayed  the  cost  of  construction,  but  gave  an  endow- 
ment to  assist  in  its  upkeep.  It  is  intended  to  serve  the 
needs  of  the  smaller  builders  who  have  not  tanks  of  their 
own,  and  also  for  the  investigation  of  matters  of  general 
interest  to  shipbuilders,  and  for  such  tests  as  that  relating  to 
the  Hawke  and  Olympic.  In  this  last-named  case,  of  course, 
two  models  were  made,  one  to  represent  each  ship,  and  they 
were  towed  along  in  such  a  way  as  to  imitate  very  closely 
the  movements  of  the  ships  at  the  time  when  they  collided. 
It  was  as  the  result  of  these  tests  that  the  Olympic  was 
ordered  to  pay  damages  to  the  Admiralty,  it  being  held  that 
she  was  the  cause  of  the  accident. 

A  very  interesting  investigation  of  this  kind  was  recently 
carried  out  in  the  tank  at  the  United  States  Navy  Yard, 
The  port  of  New  York  consists  very  largely  of  jetties  pro- 
jecting out  from  the  banks  of  the  river.  With  the  growth 
of  the  Atlantic  liner  the  old  jetties  had  become  too  short, 
and  questions  arose  as  to  the  elongation  of  them.  If  it 
were  done,  how  would  it  effect  the  current  in  the  river,  and 
the  handling  of  shipping  generally  ?  If,  on  the  other  hand, 
it  were  not  done,  what  would  be  the  effect  of  the  ships  lying 
with  their  ends  projecting  out  into  the  stream  unprotected 
by  a  jetty. 

To  determine  these  points  the  experimental  tank  was 
converted  into  a  model  of  the  New  York  Harbour,  or  at  all 
events  of  that  part  in  connection  with  which  these  questions 
arose. 

A  false  floor  was  put  in,  so  as  to  make  the  depth  exactly 
right  in  proportion  to  the  width.  Little  model  jetties  were 
arranged  to  represent  exactly  the  real  ones,  while  against 
them  were  moored  model  vessels,  so  that  the  effect  upon 
them  could  be  observed  as  the  model  of  the  large  vessel 
was  towed  past. 

In  addition  to  this,  special  appliances  were  arranged  for 


202      SCIENTIFIC  TESTING  AND  MEASURING 

finding  out  what  the  disturbance  might  be  which  the  move- 
ment of  a  giant  liner  produces  under  the  surface  as  well  as 
above  it.  For  this  purpose  buoyant  balls  were  employed, 
moored  at  various  distances  below  the  surface,  from  which 
thin  rods  projected  upwards,  the  movement  of  which 
rendered  visible  the  movements  of  the  submerged  balls  and 
therefore  the  effects  of  the  under-water  currents. 

All  these  things  had  to  be  observed  at  one  and  the  same 
time — the  moving  model  itself,  the  models  alongside  the 
jetties,  the  commotion  on  the  surface,  the  swayings  to  and 
fro  of  the  rods  attached  to  the  submerged  floats — all,  or 
most  of  which,  at  all  events,  it  was  impossible  to  make 
self-recording.  Yet,  seeing  that  it  was  of  the  utmost  im- 
portance that  the  relations  between  all  these  things  should 
be  observed,  and  recorded  from  time  to  time  as  the  model 
was  towed  along,  it  is  evident  that  something  must  be  done, 
and  a  cunning  use  of  the  kinematograph  solved  the  problem 
quite  easily.  At  various  points  commanding  a  good  view 
of  the  model  harbour  and  its  shipping  these  machines  were 
placed,  and  so  several  series  of  photographs  were  obtained, 
by  the  study  of  which  all  the  different  movements  could  be 
seen  and  compared.  A  large  dial  too  was  rigged  up  upon 
the  travelling  carriage  by  which  the  model  was  towed,  a 
finger  on  which  denoted  the  distance  which  the  carriage  had 
travelled  at  any  moment.  This  large  dial  came  into  each 
photograph,  of  course,  and  so  each  picture  bore  upon  itself 
a  clear  record  of  that  particular  moment  in  the  voyage  of 
the  model  to  which  it  referred. 

Thus  we  see  an  instance  of  how  the  very  latest  and  most 
up-to-date  methods  of  amusement  are  sometimes  applied 
to  serve  very  practical  purposes. 

Akin  to  the  experiments  upon  ships  are  aerial  experiments 
to  determine  matters  connected  with  the  navigation  of  the 
air.  At  Barrow-in-Furness  the  great  firm  of  Vickers,  ship- 
builders and  armament  manufacturers,  and  latterly  builders 
of  aerial  craft  for  the  British  Admiralty,  have  erected 
a  machine  for  testing  the  efficiency  of  aerial  propellers 


SCIENTIFIC  TESTING  AND  MEASURING      208 

and  other  things  of  a  kindred  nature.  Upon  the  top 
of  a  tall  tower  there  is  pivoted  a  long  arm  of  light  iron 
framework.  To  the  end  of  this  a  propeller  can  be  fixed,  so 
that  as  the  arm  revolves  there  is  produced  almost  exactly 
the  same  conditions  as  those  which  prevail  when  a  propeller 
drives  an  aeroplane  or  steerable  balloon. 

By  means  of  suitable  mechanism  the  propeller  can  be 
turned  at  any  desired  speed,  with  the  result  that  it  drives 
the  arm  round  and  round  upon  its  pivot  on  the  top  of  the 
tower.  The  force  which  the  propeller  thus  exerts  can  easily 
be  measured,  and  so  can  be  determined  such  questions  as  the 
most  efficient  speed  for  each  type  of  propeller,  the  power 
which  any  particular  one  can  develop,  the  best  form  for 
each  particular  need,  and  so  on. 

Materials,  too,  require  the  most  careful  testing,  in  order 
that  they  may  be  put  to  the  best  possible  use  in  modern 
machinery  and  structures.  For  example,  anyone  can 
measure  the  strength  of  a  spring,  but  what  do  we  know  as 
to  its  lasting  power  ?  Springs  often  have  to  form  part  of  a 
machine  in  which  they  are  stretched  and  compressed  millions 
of  times,  and  the  question  arises  as  to  what  is  the  best  shape 
and  material  for  the  purpose.  If  may  be  that  the  spring 
which  works  best  a  few  times  will  be  the  first  to  become 
"  weary,"  for  with  repeated  strain  such  things  as  steel 
get  tired,  just  as  the  human  frame  does.  Now  that  is  a 
matter  which  will  yield  to  no  calculation,  the  only  way  to 
determine  it  is  actual  test.  So  a  mechanism  has  to  be 
employed  which  will  extend  and  compress  the  spring  over 
and  over  again,  just  as  it  will  be  in  actual  use,  with  a  counter 
of  the  nature  of  a  cyclometer  to  count  how  many  times  it 
has  been  subjected  to  this  distortion.  Then  the  apparatus 
is  set  going  and  left  to  itself  for  hours,  or  even  for  days, 
during  which  time  it  may  work  the  spring  millions  of  times. 
This  may  go  on  until  it  breaks,  or  else  it  may  be  done  a  pre- 
arranged number  of  times,  and  then  the  spring  taken  out 
and  tested  by  other  means  to  see  how  its  strength  has  been 
affected. 


204      SCIENTIFIC  TESTING  AND  MEASURING 

Metal  bars  are  often  subjected  to  sudden  blows,  light  in 
themselves  but  oft  repeated.  The  point  to  be  determined 
then  is  how  many  times  the  blow  may  fall  before  permanent 
injury  is  done  to  the  bar.  To  investigate  such  matters  we 
have  the  "  repeated-impact "  machine.  The  bar  is  held 
in  a  suitable  holder,  under  a  hammer  which  gives  it  a  blow, 
the  force  of  which  can  be  easily  regulated,  at  regular  intervals, 
the  number  of  blows  being  counted  by  a  suitable  recording 
mechanism.  Ultimately  the  bar  breaks,  under  a  blow  the 
like  of  which  it  can  endure  singly  without  any  apparent 
strain  at  all.  The  machine,  by  the  way,  can  be  caused  to 
turn  the  bar  round  to  some  degree  after  each  blow,  so  that 
it  is  struck  from  all  directions  in  succession. 

The  microscope,  too,  has  established  its  place  in  the  test- 
ing laboratory.  It  is  a  very  valuable  adjunct  to  chemical 
and  mechanical  tests. 

Suppose,  for  example,  that  a  bar  of  steel  is  being  investi- 
gated ;  it  can  be  put  into  a  machine  and  pulled  until  it 
breaks  in  two.  The  machine  registers  the  amount  of  the 
pull  which  was  applied.  Or  a  small  piece  can  be  put  under 
a  press  and  compressed  to  any  desired  degree.  It  can  also 
be  tested  by  impact  or  even  pulled  apart  by  a  sudden  blow, 
as  described  in  Mechanical  Inventions  of  To-day.  The  bar 
can  be  supported  by  its  ends  and  loaded  or  pulled  down  in 
the  centre,  so  that  its  power  of  resisting  bending  can  be 
determined.  It  can  be  judged,  too,  from  its  chemical  com- 
position. Steel,  in  particular,  depends  for  its  properties 
very  largely  upon  its  chemical  composition.  The  difference 
between  cast-iron,  wrought-iron  and  steel,  also  the  differences 
between  the  innumerable  varieties  of  steel,  are  due  almost 
entirely  to  the  admixture  of  a  certain  percentage  of  carbon 
with  the  metal.  This  can  be  ascertained  by  chemical 
analysis.  This  form  of  inquiry  has  the  advantage  over  the 
more  purely  mechanical  methods  in  that  the  latter,  for  the 
most  part,  have  to  be  applied  to  the  bar  as  a  whole,  whereas 
the  quality  may  vary  in  different  parts,  the  surface  in 
particular  being  liable  to  differ  from  the  interior.  In  such 


SCIENTIFIC  TESTING  AND  MEASURING      205 

cases,  one  analysis  can  be  made  of  a  piece  cut  from  the 
surface  and  another  of  a  piece  from  the  centre. 

And  it  is  here,  too,  that  microscopical  analysis  comes  in. 
For  this  purpose  a  piece  is  sawn  off  the  bar,  and  the  end 
ground  perfectly  smooth.  This  is  then  washed  in  a  suitable 
chemical,  such  as  a  mild  acid,  which  acts  differently  upon 
the  different  materials  of  which  the  "  metal "  is  built  up, 
thereby  rendering  them  visible  one  from  another.  A  photo- 
graph taken  through  a  microscope  then  shows  the  structure 
of  the  metal ;  how  the  different  constituents  are  built 
together. 

This  is  known  as  metallographic  testing,  and  its  advan- 
tage as  compared  with  chemical  analysis  is  that  the  latter 
shows,  as  we  might  say,  what  are  the  bricks  of  which  the 
thing  is  built,  while  the  former  shows  how  the  bricks  are 
arranged.  Indeed  it  is  hardly  correct  to  speak  of  the 
advantage  or  superiority  of  one  over  the  other,  since  each 
is  the  complement  of  the  other,  supplying  the  information 
which  the  other  fails  to  give. 

And  there  are  other  mechanical  tests  which  have  not  yet 
been  mentioned.  There  are  machines  which  twist  a  bar  so 
as  to  discover  its  power  to  resist  torsion,  there  are  others 
which  apply  a  downward  pressure  on  one  part  of  the  bar 
and  an  upward  one  on  an  adjacent  part,  so  as  to  show  its 
capabilities  in  withstanding  shearing  strain. 

Moreover,  many  of  these  tests  are  nowadays,  in  a  well- 
equipped  testing-house,  carried  out  in  conjunction  with  the 
use  of  heat.  It  stands  to  reason  that  a  part  of  a  machine 
which  will  have  to  work  under  considerable  heat  may  have 
to  be  of  different  material  from  a  part  which  works  under 
a  normal  temperature.  In  some  cases  the  bar  is  surrounded 
by  a  spiral  wire  through  which  electric  current  is  passing, 
and  by  the  regulation  of  this  current  any  desired  temperature 
can  be  set  up  in  the  bar.  Or  it  may  be  placed  in  a  bath  of 
hot  oil  in  such  a  way  that  the  bar  shall  be  raised  to  any 
temperature  required,  without  interfering  with  the  machinery 
which  exerts  the  tension  or  pressure,  or  whatever  it  be. 


206      SCIENTIFIC  TESTING  AND  MEASURING 

Years  ago  such  elaborate  tests  as  these  were  never  thought 
of.  There  are  certain  well-known  figures,  to  be  found  in  all 
engineering  text-books,  which  give  what  stresses  different 
materials  ought  to  be  able  to  stand,  and  these  were,  and  are 
still,  to  a  large  extent,  relied  upon,  it  being  taken  for  granted 
that  the  material  used  will  be  up  to  the  average  standard. 
In  large  and  important  works,  however,  the  testing  has  been 
developed  upon  scientific  lines,  so  that  it  is  known  from  actual 
experiment  what  each  particular  thing  is  capable  of.  This 
not  only  means  security  but  economy,  for  it  is  sometimes 
found  that  a  substance  is  stronger  than  it  is  thought  to  be, 
and  so  things  made  of  it  can  be  designed  to  give  the  requisite 
strength  lighter  and  cheaper  than  they  would  have  been 
otherwise. 

Some  of  the  machines  employed  are  of  enormous  strength, 
capable  of  exerting  a  pull  or  a  compression  of,  it  may  be, 
100  tons  or  more.  They  are  often  made,  too,  with  self- 
recording  appliances,  whereby  the  course  of  the  test  is  set 
down  automatically  upon  a  chart.  For  example,  when  a 
bar  is  being  tested  for  tension,  it  is  desirable  to  know  riot 
only  the  actual  pull  under  which  it  came  in  two,  but  the 
behaviour  of  the  test  piece  during  the  period  before  that. 
It  begins  to  stretch  as  soon  as  the  tension  is  applied,  theo- 
retically at  all  events,  and  if  the  metal  were  perfectly  ductile 
it  would  stretch  continuously  as  the  load  increases,  until  at 
last  the  breaking  stress  is  reached.  But  in  actual  practice 
it  probably  stretches  somewhat  by  fits  and  starts,  and  a 
record  of  that  fact  will  be  of  great  value  in  estimating  the 
strength  of  the  material  in  actual  work.  For  such,  an 
automatically  made  record,  which  can  be  studied  at  leisure, 
is  of  the  utmost  importance. 

But  perhaps  the  finest  instance  of  scientific  methods 
in  manufacture  is  to  be  found  in  the  methods  by  which 
standard  parts  of  machines  are  measured,  so  as  to  ensure 
that  they  shall  be  interchangeable. 

It  may  surprise  the  casual  reader  to  be  told  that  an 
absolutely  exact  measurement  is  an  impossibility.  It  is 


SCIENTIFIC  TESTING  AND  MEASURING      207 

safe  to  say  that  out  of  a  million  similar  articles — articles 
made  with  the  intention  that  they  shall  be  exactly  alike — 
there  are  no  two  which  are,  in  fact,  absolutely  similar.  They 
may  be  made  with  the  same  machines  and  the  same  tools, 
handled  by  the  same  man,  but  machines  and  tools  wear  or 
get  out  of  adjustment,  while  man's  liability  to  err  is  pro- 
verbial. Astronomers  are  the  greatest  experts  in  the  art  of 
measurement,  and  they  recognise  the  possibility,  nay,  the 
probability,  of  error  so  frankly  as  to  make  every  measure- 
ment several  times  over ;  if  it  be  an  important  one  they 
make  it,  if  possible,  a  great  many  times  over,  and  then 
take  the  average  of  the  results.  By  this  means  they 
eliminate,  to  a  certain  extent  at  any  rate,  the  error  which 
cannot  be  avoided.  That  process  is  to  allow  for  errors  on 
the  part  of  their  instruments,  for  the  most  part.  To  deal 
with  personal  errors  another  method  is  used  as  well,  for  it 
is  known  that  some  observers  have  a  natural  tendency  to  err 
on  one  side  more  or  less,  while  others  tend  to  make  mistakes 
in  some  degree  on  the  other  side.  This  tendency  to  err  is 
known  as  the  "personal  equation"  of  the  observer,  and 
there  are  machines  and  tests  by  which  the  personal  equation 
of  each  man  can  be  determined,  or  perhaps  it  would  be  more 
correct  to  say  estimated,  so  that  in  all  observations  made  by 
him  the  proper  allowance  can  be  added  or  deducted. 

But  of  course  it  would  be  extremely  difficult  to  apply  such 
methods  in  a  workshop.  It  would  never  do  to  have  to 
measure  everything  several  times  over,  hoping  that  the 
average  would  come  out  in  such  manner  as  to  indicate  that 
the  thing  being  measured  was  the  size  required.  Instead, 
therefore,  of  wasting  time  seeking  an  accuracy  which  is 
known  to  be  unattainable,  the  manufacturing  engineer 
adopts  a  scientific  system  of  measurement  wherein  a  certain 
amount  of  inaccuracy  is  determined  upon  as  permissible, 
and  then  simple  appliances  are  used  to  see  that  it  does,  in 
fact,  fall  within  those  limits.  For  instance,  a  round  bar  is 
to  be  made,  say,  an  inch  in  diameter.  Now  we  know  from 
what  has  just  been  said  that,  when  made,  we  have  no  means 


208      SCIENTIFIC  TESTING  AND  MEASURING 

of  telling  whether  the  bar  is  really  and  truly  an  inch  in 
diameter  or  not.  We  consider,  then,  what  it  is  for,  and 
decide,  say,  that  it  will  be  near  enough  so  long  as  we  are  sure 
that  it  is  not  larger  than  one  inch  plus  one  thousandth,  nor 
less  than  one  inch  minus  one  thousandth.  So  long  as  it 
does  not  exceed  or  fall  short  of  its  reputed  size  by  more  than 
one  thousandth  of  an  inch,  then  we  know  that  it  will  answer 
its  purpose. 

Now,  having  come  to  that  decision,  we  can  build  up  a 
system  upon  which  any  intelligent  workman  can  proceed, 
with  the  result  that  all  the  inch  bars  which  he  makes  will 
be  the  same  size  within  the  limits  of  T&TTG  over  or  under, 
so  that  the  greatest  possible  difference  between  any  two  will 
be  Tthr. 

This  system  involves  the  use  of  two  gauges  for  every  size. 
The  man  employed  upon  making  one-inch  bars  has  a  plate 
with  a  hole  in  it  l-nnnr  inches  in  diameter  and  another 
hole  Tinnr  of  an  inch  in  diameter.  One  of  these  is  the 
44  go  in"  gauge;  the  other  is  the  "not  go  in."  So 
that  all  he  has  to  do,  in  order  to  be  quite  sure  that 
his  work  is  right,  is  to  see  that  it  can  be  poked  through 
one  of  these  holes,  but  not  through  the  other.  No 
trouble  at  all,  it  will  be  observed,  adjusting  fine  measuring 
appliances,  simply  a  plate  with  two  holes  in  it,  and 
the  workman  can  be  sure  that  he  is  turning  out  articles 
every  one  of  which  is  practically  correct,  with  no  variation 
beyond  a  slight  inequality  too  small  to  matter. 

And  probably  at  some  other  part  of  the  factory  there  is  a 
man  making  articles  each  of  which  has  a  hole  in  it,  into 
which  this  bar  must  fit.  How  does  he  manage  ?  He  is 
provided  with  a  gauge  somewhat  the  shape  of  a  dumb-bell, 
one  end  of  which  is  slightly  larger  than  the  other.  One  is  the 
"  go  in  "  end,  the  other  the  "  not  go  in  "  end.  If  the  hole 
which  he  makes  will  permit  the  former  to  enter,  but  will 
refuse  admittance  to  the  latter,  then  he  knows  that  that 
hole  is  sufficiently  near  its  reputed  size  to  answer  its 
purpose. 


SCIENTIFIC  TESTING  AND  MEASURING      209 

In  the  instances  mentioned,  a  thousandth  of  an  inch 
either  way  has  been  mentioned  as  the  limit  of  inaccuracy,  or 
the  "  tolerance,"  as  it  is  sometimes  termed,  but  often  the 
limits  are  much  narrower  than  that.  The  gauges  themselves 
are  a  case  in  point,  for  they  must  be  true  within,  say,  a  ten- 
thousandth,  or  even  less.  And  they  too  are  checked  by 
master  gauges  of  a  finer  degree  of  accuracy  still,  being 
made  by  the  most  laborious  methods,  and  checked  over  and 
over  again,  so  as  to  reach  the  utmost  limits  in  the  way 
of  correctness. 

So  this  methodical  "  scientific  "  system  of  "  limit  gauges  " 
is  based  upon  the  principle  of  having  one  gauge  limiting  the 
error  one  way  and  another  defining  it  in  the  other.  Any- 
thing simpler  or  more  effective  it  would  be  impossible  to 
conceive.  It  is  due  very  largely  to  this  system  that  many 
manufactured  articles  are  now  so  much  cheaper  than  they 
used  to  be.  For  it  enables  each  individual  part  to  be  made 
wholesale  on  a  large  scale,  by  machines  specially  adapted 
to  the  work,  operated  by  men  specially  trained  to  work  them, 
with  the  practical  certainty  that  these  parts  when  assembled 
together  will  fit  each  other. 

In  conclusion,  there  is  another  very  interesting  instrument 
which  was  first  made  for  a  purely  utilitarian  use — namely, 
the  investigation  of  the  methods  of  making  coloured  glass — 
but  which  has  since  been  applied  to  some  interesting  prob- 
lems in  pure  science.  It  is  called  the  "  ultra-microscope." 

It  must  first  be  pointed  out  that  there  is  a  limit  to  the 
power  of  the  ordinary  microsocpe,  beyond  which  the  skill 
of  the  optician  cannot  go.  He  is  baffled  at  that  point  not 
because  of  any  lack  of  ability  on  his  own  part,  but  because 
of  the  nature  of  light  itself.  An  opaque  object,  unless  it  be 
self-luminous,  which  few  things  are,  can  only  be  seen  by 
reflected  light.  Generally  speaking,  we  see  things  because 
they  reflect  in  some  degree  the  light  which  falls  upon  them. 
But  light  consists  of  waves,  and  when  we  reach  an  object 
so  minute  that  its  diameter  is  about  half  the  wave-length  of 
light,  then  we  cannot  see  it  because  it  is  unable  to  reflect 


210      SCIENTIFIC  TESTING  AND  MEASURING 

the  light  on  account  of  its  smallness.  We  can  see  this  any 
day  by  the  seaside,  or  by  a  river  or  large  pond.  There  it 
is  evident  that  the  waves  and  ripples  are  reflected  by  such 
things  as  large  stones,  wood  posts  or  anything  of  any  size 
which  come  in  their  way  ;  but  when  a  wave  encounters  an 
object  much  smaller  than  itself  it  simply  swallows  it  up, 
as  it  were,  flows  all  over  it  or  around  it,  without  being  in  any 
way  reflected  by  it.  And  it  is  just  the  same  with  the  waves 
of  light ;  they  are  unaffected  by  obstacles  below  a  certain 
size,  and  so  are  not  reflected  by  them.  For  this  reason 
things  smaller  than  about  a  seven-thousandth  of  a  milli- 
metre cannot  possibly  be  seen  by  a  microscope  in  the  ordinary 
way. 

But  if  an  object  can  be  made  self-luminous,  then  it  can 
be  seen,  whatever  its  size,  if  the  magnifying  power  of  the 
microscope  be  great  enough.  So  this  ultra -microscope,  as 
it  is  called,  is  really  an  ordinary  microscope  of  the  highest 
power  possible,  with  an  added  apparatus  for  making  the 
tiny  particles  which  are  being  sought  for  self-luminous. 
This  is  done  by  directing  upon  them  a  pencil  of  light  of 
exceeding  intensity.  Generated  by  powerful  arc  lamps, 
the  light  is  concentrated  by  a  system  of  lenses  until  it  is  of 
an  almost  incredible  brightness,  after  which  it  falls  upon 
the  object. 

Now  at  first  sight  this  seems  to  be  no  different  from  the 
usual  procedure  with  a  microscope,  and  there  appears  to  be 
no  reason  why  it  should  be  more  successful,  but  the  explana- 
tion is  this  :  light  is  a  form  of  energy,  and  the  waves  of  this 
very  intense  beam,  falling  upon  the  object,  throw  it  into  a 
state  of  violent  agitation,  by  virtue  of  which  it  shines,  not 
with  reflected  light,  but  with  light  of  its  own.  It  is  not  that 
the  waves  are  reflected,  but  that  they  so  shake  up  the 
particle  that  it  gives  off  light  waves  itself.  And  thus  it 
comes  within  the  range  of  human  vision. 

In  this  way,  not  only  have  the  very  small  particles  of 
colouring  matter  in  glass  been  seen  individually,  but  it  is 
thought  that  the  actual  molecules  of  matter  have  been  seen, 


SCIENTIFIC  TESTING  AND  MEASURING      211 

or  if  not  the  molecules  individually,  little  groups  of  molecules, 
dancing  and  capering  about,  just  as  scientific  people  for  years 
have  believed  them  to  be  doing,  although  they  could  not 
see  them.  So  here  we  have  an  instance  in  which  manufacture 
has  aided  science — an  inversion  of  the  usual  order  of  things. 


CHAPTER  XVI 

COLOUR  PHOTOGRAPHY 

PHOTOGRAPHY  has  introduced  many  of  the  general 
public  to  a  branch  of  practical  science  which  other- 
wise they  would  never  have  cared  much  about.  The 
action  of  light  upon  certain  chemicals,  the  subsequent  action 
upon  the  same  of  other  chemicals,  such  as  developers,  toning 
solutions  and  so  on,  form  a  very  well-known  region  of  the 
domain  of  science.  And  this  is,  too,  a  branch  of  chemistry 
in  which  the  practical  inventor  has  been  very  busy.  The 
efforts,  therefore,  which  have  been  made  to  invent  ways  of 
producing  photographic  pictures  which  shall  give  to  the 
objects  their  natural  colours,  will  probably  be  of  special 
interest  in  a  book  like  this. 

Of  these  there  are  two  very  well-known  systems,  and  to 
them  we  will  mainly  confine  our  attention. 

It  should  first  be  pointed  out,  however,  that  what  we 
are  discussing  is  quite  different  from  the  simple  "  ortho- 
chromatic  "  plates  which  are  used  by  many  photographers. 
These  latter  are  coated  somewhat  differently  from  other 
plates,  with  a  view  to  their  giving  a  more  realistic  picture, 
but  the  result  is  still  in  one  colour.  They  are,  in  fact,  a  little 
more  sensitive  to  differences  in  colour  than  ordinary  plates, 
so  that  colours  which  appear,  when  the  latter  are  used,  very 
much  the  same,  appear,  when  orthochromatic  plates  are 
employed,  a  little  different.  But  the  difference  in  colour  in 
the  object  photographed  is  only,  even  then,  represented  by 
a  difference  in  shade  in  the  picture.  The  object  is,  it  may 
be,  in  many  colours,  in  all  the  colours,  very  likely,  but  the 
picture  is  only  in  one. 

And  the  step  from  that  to  a  coloured  picture  is  a  very  long 

212 


COLOUR  PHOTOGRAPHY  218 

one.  True,  the  solution  of  the  problem  is  very  simple  in 
principle,  yet  the  practical  difficulties  are  so  great  that  even 
now  they  have  not  been  entirely  overcome. 

Let  us  first  of  all  examine  the  principle.  Sunlight,  by 
which  photographs  are  usually  taken,  appears  to  the  eye 
white  and  colourless.  It  is  not  really  so,  however,  as  can 
be  proved  by  analysing  it  with  the  spectroscope.  In  this 
instrument  a  flat  beam  of  light,  having  passed  through  a 
narrow  slit,  falls  upon  a  prism  of  glass,  from  which  it  emerges 
as  a  broad  band,  known  as  the  "  spectrum."  This  band 
can  be  seen  upon  a  screen,  or  can  be  examined  through  a 
telescope.  So  far  from  being  white  and  colourless,  it  consists 
of  the  most  lovely  colours.  At  one  end  of  the  spectrum  is  a 
beautiful  red,  which,  as  the  eye  travels  along,  imperceptibly 
merges  into  orange,  which  in  turn  merges  into  yellow,  after 
which  we  find  green,  blue,  indigo  and  violet,  in  the  order 
named.  These  seven  are  known  as  the  "  primary  colours," 
but  it  is  quite  a  mistake  to  suppose  that  there  are  seven 
clearly  defined  and  distinct  colours.  The  colours  so  change, 
one  into  another,  that  their  number  is  really  infinite.  The 
seven  names  indicate  seven  points  in  the  spectrum,  whereat 
the  colours  are  sufficiently  distinct  from  others  to  warrant 
a  separate  name  being  given  to  them.  We  call  the  starting 
colour  red,  for  example,  and  as  we  pass  our  eyes  along  we 
perceive  a  constant  change,  and  when  that  change  has  become 
sufficiently  pronounced  to  justify  our  doing  so,  we  call  the 
new  colour  "orange."  Continuing,  we  find  the  orange 
changing  into  something  else,  and  when  it  has  gone  far 
enough,  we  bring  in  a  third  name,  yellow,  and  so  on  to  the 
violet.  Thus  we  see  the  division  into  seven  colours  is 
arbitrary,  and  only  for  our  own  convenience,  since  the  whole 
number  of  colours  is  innumerable. 

Passing  through  a  prism  is  not,  however,  the  only  means 
by  which  white  light  can  be  split  up.  When  the  sun  shines 
upon  a  blue  flower,  for  instance,  the  blue  petals  perform  a 
partial  separation ;  they  reflect  the  blue  part  of  the  sun- 
light, and  absorb  all  the  rest.  A  red  flower  likewise 


214  COLOUR  PHOTOGRAPHY 

reflects  the  red  part  of  the  sunlight  and  absorbs  the  rest.  It 
is  because  things  can  thus  discriminate,  reflecting  some  kinds 
of  light  and  absorbing  the  remainder,  that  we  perceive  things 
in  different  colours. 

It  follows,  therefore,  that  when  we  look  upon  a  landscape, 
or  a  field  of  flowers,  we  receive  into  our  eyes  an  enormous 
variety  of  coloured  lights.  The  white  sunlight  furnishes 
each  thing  we  see  with  a  flood  of  white  light,  and  each  thing 
according  to  its  nature,  reflects  more  or  less.  A  white  flower 
reflects  the  whole,  a  pure  black  object  reflects  none,  but  the 
great  majority  of  things  reflect  some  part  or  other  of  that 
infinite  variety  of  which  white  light  really  consists. 

So  a  view  at  all  varied  sends  to  our  eyes  a  variety  of 
colours,  almost  as  manifold  as  the  colours  of  the  spectrum, 
which,  as  has  been  said,  are  infinite.  And  the  task  of 
reproducing  them,  or  even  of  producing  a  similar  general 
effect,  upon  a  piece  of  paper  seems  at  first  sight  beyond  the 
bounds  of  possibility. 

But  fortunately  there  is  a  way  by  which  we  can  produce, 
approximately  at  all  events,  the  intermediate  colours  by 
mixtures  of  the  others.  The  second  colour  of  the  spectrum, 
for  example,  orange,  can  be  obtained  by  mixing  its  neigh- 
bours on  either  hand — namely,  red  and  yellow.  We  can, 
indeed,  imitate  very  closely  the  imperceptible  change  from 
red  to  yellow  through  orange,  by  skilful  mixture  of  red  and 
yellow  pigments.  First  there  is  the  pure  red,  then  just  a 
suggestion  of  yellow  is  added  ;  more  and  more  yellow  brings 
us  to  orange ;  after  which  by  gradually  diminishing  the 
amount  of  red  we  reach  the  pure  yellow.  Next,  by  intro- 
ducing blue  pigment,  we  can  gradually  change  the  yellow 
into  green,  and  further  manipulation  of  the  same  two  colours 
will  lead  us  on  to  pure  blue.  Indeed  by  mixtures  of  red, 
yellow  and  blue  we  can  obtain  almost  all  the  perceptible 
varieties  of  colour. 

And  it  must  be  remembered  that  when,  by  mixing  blue 
and  yellow  pigments,  we  get  the  effect  of  green,  that  is  only 
the  result  of  an  optical  illusion.  The  particles  of  which 


COLOUR  PHOTOGRAPHY  215 

the  yellow  pigment  is  made  remain  yellow,  and  the  particles 
of  blue  remain  blue.  The  one  sort  reflect  yellow  light  to 
our  eyes,  the  other  sort  reflect  blue  light,  and  owing  to  what 
in  one  sense  may  be  called  a  defect  in  our  vision,  these  two 
mingling  together  look  as  if  the  whole  were  green.  In 
the  spectrum  we  see  real  green  light ;  from  green  paint  made 
by  mixing  yellow  and  blue,  we  only  see  an  imitation  or 
artificial  green.  If  the  particles  were  large  enough,  we  should 
see  the  yellow  and  the  blue  ones  quite  separate,  but  since 
they  are  too  small  for  us  to  see  at  all,  except  in  the  mass,  our 
eyes  blend  the  whole  together  into  the  intermediate  colour. 

Thus  we  see  that,  although  the  variety  of  colours  is  infinite, 
we  can  for  practical  purposes  reproduce  as  much  difference 
as  our  eyes  can  perceive  by  the  judicious  blending  of  three 
— namely,  red,  yellow  and  blue. 

And  there  is  a  further  fortunate  fact — we  can  filter  light. 
The  red  glass  with  which  the  photographer  covers  his  dark- 
room lamp  looks  red,  and  throws  a  red  light  into  the  room, 
because  it  is  acting  as  a  filter  to  the  light  proceeding  from 
the  lamp  behind  it.  The  lamp  is  sending  out  light  of  many 
colours,  but  the  glass  is  only  transparent  to  the  red.  It 
holds  up  all  the  others  but  lets  the  red  pass  freely.  So  if 
we  were  to  take  a  photograph  through  a  red  screen,  we 
should  get  on  the  plate  only  those  parts  which  were  more 
or  less  red  in  colour.  For  example,  if  we  thus  photographed 
a  group  of  three  flowers,  one  red,  one  orange  and  one  yellow, 
the  red  one  would  come  out  prominently,  the  orange  one 
would  come  out  faintly,  and  the  yellow  one  not  at  all. 

Then  suppose  we  took  the  same  picture  again  through  a 
yellow  screen.  In  that  case  the  yellow  flower  would  be 
prominent,  the  orange  would  again  be  faint,  but  the  red 
would  be  absent. 

Having  got,  in  imagination,  two  such  negatives,  let  us 
make  two  carbon  prints,  one  off  each.  And  let  the  print 
off  the  first  negative  be  red,  while  that  off  the  second  is 
yellow.  Let  each  be,  in  fact,  of  the  same  colour  as  the 
screen  through  which  the  picture  was  taken.  Finally,  let 


216  COLOUR  PHOTOGRAPHY 

the  two  films  be  placed  in  contact  one  upon  the  other.  On 
holding  the  two  up  to  the  light,  what  should  we  see  ? 

We  should  see  a  red  flower,  for  there  would  be  a  red 
flower  clearly  defined  upon  one  film  coinciding  with  a  blank 
transparent  space  upon  the  other  film.  We  should  see,  too, 
a  yellow  flower,  for  a  clearly  defined  yellow  flower  on  the 
second  film  would  coincide  with  a  clear  space  upon  the  first. 
We  should  see  also  an  orange-coloured  flower,  for  there  would 
be  a  faint  red  image  of  it,  and  a  faint  yellow  image  of  it, 
one  on  each  film,  lying  one  over  the  other,  producing  the 
same  effect  as  a  mixture  of  yellow  and  red  pigments.  Thus 
by  taking  two  negatives  through  two  coloured  screens,  and 
then  colouring  the  prints  to  correspond,  we  can  obtain  three 
colours  in  the  finished  picture. 

By  taking  a  third  negative,  through  a  blue  screen,  we 
could  add  immensely  to  the  range  of  colours  obtainable. 
Indeed,  with  three  films,  red,  yellow  and  blue  respectively, 
made  through  three  screens  of  the  same  colour,  a  variety  of 
colours  practically  infinite  can  be  obtained. 

So  the  principle  is  quite  simple ;  the  difficulty  is  in 
carrying  it  out.  For  the  three  kinds  of  light  have  not  the 
same  photographic  power,  and  so  to  avoid  upsetting  the 
"  balance "  of  the  colours  different  exposures  would  be 
required  for  each.  Then  there  is  the  difficulty  of  so  manipula- 
ting the  films  as  to  get  them  one  over  another  exactly. 
Anyone  who  has  tried  the  handling  of  carbon  prints  will 
readily  realise  how  difficult  this  would  be.  It  is  possible 
and  has  been  done,  but  the  process  is  too  uncertain  and  too 
laborious  to  be  of  general  use. 

But  the  same  result  can  be  attained  more  or  less  auto- 
matically, as  the  following  descriptions  will  show. 

Let  us  turn  to  the  Lumiere  autochrome  process,  by  which 
the  results  desired  can  be  in  a  large  measure  attained  by 
methods  of  manipulation  comparatively  simple. 

The  plates  used  for  this  are  of  a  very  special  nature.  In 
the  first  place,  there  is  the  basis  of  glass,  but  upon  that  there 
is  laid  what  we  might  term  the  selective  screen.  This 


Bype* 


Ihe  Mining  Engineering  Co.,  Ltd.,  Sheffield 

PNEUMATIC  HAMMER  DRILL 


This  tool  is  used  by  miners  for  making  holes  in  hard  rock,  preliminary  to 
blasting.  Note  the  spray  of  water,  which  prevents  the  stone  dust  rising  and 
getting  into  the  miner's  lungs.— See  p.  220 


COLOUR  PHOTOGRAPHY  217 

is  a  layer  of  starch  grains,  of  exceeding  smallness.  The 
size  of  them  is  as  little  as  a  half  a  thousandth  of  an  inch  and 
there  are  about  four  millions  of  them  on  every  square  inch 
of  plate.  Next,  upon  the  screen  of  starch  grains  is  a  layer 
of  waterproof  varnish,  while  over  that  is  the  ordinary 
sensitive  emulsion  such  as  forms  the  essential  part  of  the 
usual  non-colour  plate. 

Now  the  starch  grains  which  form  the  screen  are,  before 
they  are  laid  on,  stained  in  three  colours.  Some  are  blue, 
some  red,  and  some  a  yellowish-green,  which  experience  shows 
is  preferable  to  pure  yellow.  The  differently  coloured  grains 
are  well  mixed,  and  when  the  screen  is  held  to  the  light  and 
looked  through  the  effect  is  almost  that  of  clear  glass.  That 
is  because  red  rays  from  the  red  grains,  and  green  and  blue 
rays  from  the  grains  of  those  colours,  all  proceed  to  the  eye 
mingled  together. 

This  plate  is  placed  in  the  camera  differently  from  the 
usual  way,  since  the  glass  side  is  turned  towards  the  lens. 
The  light,  therefore,  after  entering  the  camera,  passes 
through  the  glass,  then  through  the  screen,  and  finally  falls 
upon  the  sensitive  film. 

Suppose,  then,  that  the  camera  were  pointed  to  a  red 
wall ;  red  light  would  fall  upon  the  plate  and,  passing  through 
the  red  grains,  would  act  upon  the  sensitive  film  behind  them. 
The  blue  and  green  grains,  on  the  other  hand,  would  stop 
those  rays  which  fell  upon  them,  and  so  those  parts  of  the 
sensitive  film  which  they  cover  would  remain  unaffected 
by  light.  Then,  if  that  plate  were  to  be  developed,  a  dark, 
opaque  spot  would  be  produced  upon  the  film  under  each 
red  grain,  the  film  under  the  other  grains  remaining  trans- 
parent. Hence,  when  held  up  to  the  light  and  looked 
through,  the  plate  would  appear  a  greenish-blue,  for  all  the 
red  grains  would  be  covered  up. 

In  like  manner,  if  the  wall  were  blue  instead  of  red,  a 
greenish-red  plate  would  result,  while  if  it  were  green,  the 
plate  would  be  a  purple,  the  result  of  the  combination  of 
red  and  blue. 


218  COLOUR  PHOTOGRAPHY 

But  this,  it  will  be  seen,  is  a  topsy-turvy  effect,  the  exact 
opposite  of  what  we  want,  so  that  it  is  fortunate  that  by  a 
simple  chemical  method  we  can  set  it  right.  After  a  first 
development  in  the  ordinary  way  the  plate  is  placed  in 
another  bath  and  exposed  to  strong  daylight,  with  the  result 
that  those  parts  which  were  darkened  by  the  first  develop- 
ment become  clear  and  the  parts  which  were  clear  become 
opaque.  Thus,  after  this  twofold  development  of  the 
photograph  of  the  red  wall,  we  find  ourselves  in  possession 
of  a  red  plate,  in  which  only  the  red  grains  are  visible,  since 
all  the  others  are  covered  up  by  opaque  parts  of  the  sensitive 
film.  The  photograph  of  the  blue  wall  will  also,  after  it  has 
been  subjected  to  the  double  development,  show  blue  only, 
and  the  same  with  the  green. 

But  suppose  that  instead  of  a  red  wall  or  a  blue  wall  we 
focus  our  camera  upon  one  which  is  half  red  and  half  blue. 
Then  it  is  easy  to  perceive  that  we  shall  get  a  plate  which 
is  half  one  colour  and  half  the  other.  Moreover,  it  follows 
that  a  wall  covered  with  a  mosaic  of  red,  blue  and  green 
would  give  us  a  plate  duly  coloured  in  the  same  way. 

But  when  we  go  a  step  further  and  photograph,  say,  a 
landscape,  which  may  contain  a  vast  range  of  colours,  we 
find  a  difficulty  in  believing  that  they  can  all  be  rendered 
by  the  simple  process  of  covering  or  leaving  uncovered  grains 
either  blue,  red  or  green.  It  can  be  done,  however,  since  the 
other  colours  may  be  made  up  of  two  or  more  of  these  three 
in  varying  proportions.  For  example,  should  there  be 
something  in  the  landscape  of  a  darker,  more  blue,  shade  of 
green  than  the  green  grains,  then  the  light  proceeding  from 
that  object,  while  passing  freely  through  the  green  grains 
upon  which  it  falls,  will  slightly  penetrate  the  neighbouring 
blue  ones  as  well,  and  so  at  that  point  on  the  plate  there  will 
be  not  only  green  grains  visible,  but  some  of  the  blue  grains 
partly  visible  also.  The  light  from  the  blue  grains  will 
enter  the  eye  along  with  that  from  the  green  grains,  and  by 
so  doing  will  add  just  that  amount  of  blue  to  the  green  as 
to  give  it  the  right  shade. 


COLOUR  PHOTOGRAPHY  219 

After  this  manner  is  the  whole  picture  built  up.  It  is,  of 
course,  really  a  mosaic,  consisting  entirely  of  little  coloured 
patches,  but  since  they  are  so  small  none  can  be  seen  in- 
dividually, all  merging  together  in  the  eye  so  as  to  form 
a  picture  in  which  colours  change  imperceptibly  from  one 
into  another. 

To  sum  up,  then,  what  happens  is  this.  We  start  with  a 
layer  of  coloured  grains  ;  the  action  of  taking  and  developing 
the  photograph  covers  up  some  of  these  grains  and  leaves 
others  exposed,  and  the  action  of  the  light  is  such  that  those 
which  are  left  visible  produce  a  picture  closely  resembling 
the  original,  not  only  in  form  but  in  colour. 

But  there  is  one  other  interesting  point  about  this  process 
which  deserves  mention.  The  differently  coloured  lights  are 
not  of  the  same  power  photographically.  Red  light,  as  we 
know  well,  is  very  weak  in  this  respect,  wherefore,  we  use 
it  in  the  dark-room.  A  faint  red  light  will  have  no  percep- 
tible effect  upon  a  plate  unless  it  be  exposed  to  it  for  some 
time.  Blue  light,  on  the  other  hand,  is  very  active,  and  were 
the  blue  and  red  lights  to  be  allowed  to  act  equally  on  the 
autochrome  plate,  the  result  would  be  much  too  blue.  It  is 
therefore  necessary  to  handicap  the  blue  light,  as  it  were, 
by  placing  a  "  reddish-yellowish  "  screen  either  just  in  front 
of,  or  just  behind,  the  lens  to  cut  off  a  proportion  of  the  blue 
rays. 

The  other  very  successful  process  is  known  as  the  Dufay 
dioptichrome  process.  It  differs  very  little  from  the  Lumiere 
except  in  detail,  the  selective  screen  being  formed  of  small 
coloured  squares  instead  of  by  a  mass  of  little  grains. 

In  both,  it  will  be  noticed,  the  result  is  a  single  positive. 
It  is  not,  as  in  ordinary  photography,  a  negative  off  which 
any  desired  number  of  positive  prints  can  be  made.  And, 
moreover,  it  is  a  transparency  :  it  cannot  be  viewed  except 
by  light  shining  through  it.  The  results  are,  however, 
extremely  beautiful,  when  well  done,  and  anyone  who  cares 
to  try  either  of  these  methods  of  working  will  be  well  repaid 
for  the  trouble  involved. 


CHAPTER  XVII 

HOW  SCIENCE  AIDS   THE  STRICKEN   COLLIER 

NOTHING  is  more  characteristic  of  the  present  age 
than  the  care  which  is,  quite  rightly,  expended  upon 
the  comfort  and  safety  of  those  who  do  the  manual 
labour  of  the  community .  The  stores  of  scientific  knowledge 
and  skill  are  drawn  upon  freely  for  this  end,  and  some  very 
interesting  examples  can  be  given  of  the  truly  scientific 
methods  which  have  been  evolved,  not  only  for  preventing 
injuries  of  any  kind,  but  for  succouring  those  who  may, 
despite  those  precautions,  fall  victims  to  disease  or  accident. 

An  example  has  already  been  given  of  the  scientific 
investigation  into  the  nature  of  colliery  explosions  and  the 
best  means  of  preventing  them.  We  have  seen  there  how 
expense  has  been  poured  out  lavishly  in  fitting  up  the 
experimental  gallery  or  artificial  pit,  and  how  the  most 
cunning  mechanical  and  electrical  devices  have  been  pressed 
into  the  service  in  order  to  find  out  just  what  happens  when 
an  explosion  occurs.  It  has  been  related  how  these  investiga- 
tions have  revealed  with  certainty  the  true  cause  of  the 
explosions  and  thereby  led  the  way  to  their  prevention. 

But  with  it  all  there  is  still  an  occasional  disaster,  occurring, 
sometimes,  at  the  best  and  most  carefully  managed  collieries. 
And  therefore  it  is  still  necessary  to  provide  for  rescuing 
the  unfortunate  men  who  are  affected. 

It  is  worth  remark,  here,  that  colliery  explosions  are,  all 
things  considered,  a  very  rare  occurrence.  Because  of  their 
dramatic  suddenness,  and  the  number  of  lives  which  are 
commonly  lost  in  a  single  disaster,  we  are  apt  to  magnify 
their  severity  in  our  minds  and  to  picture  the  life  of  the 
miner  as  a  very  hazardous  one.  In  point  of  fact,  the  ex- 

220 


HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER     221 

pectation  of  life,  as  the  insurance  people  call  it,  is  quite  as 
great  among  the  coal -miners  as  among  any  class  of  manual 
labour.  And  of  those  who  do  meet  an  untimely  end  there 
are  more  lost  through  isolated  accidents,  involving  one  or 
two  men,  than  in  the  great  disasters. 

To  meet  these  isolated  cases  science  is  almost  powerless. 
For  the  most  part,  they  are  due  to  falls  of  material  from  the 
roof  of  the  mine,  or  some  simple  accident  of  that  kind,  caused 
by  an  error  of  judgment  or  lack  of  care  on  the  part  of  fellow- 
workmen,  and  the  only  safeguard  against  such  is  the  most 
careful  and  systematic  supervision,  which,  in  Great  Britain 
at  all  events,  is  rigidly  applied.  The  underground  staff  are 
very  carefully  organised  with  this  end  in  view,  and  the  whole 
is  supervised  by  Government  inspectors.  No  amount  of 
scientific  investigation  or  invention  will  help  much  in  these 
matters. 

With  the  explosion  or  fire,  however,  it  is  different,  for  there 
subtle  forces  and  strange  chemical  influences  come  into  play 
with  which  science  is  specially  well  fitted  to  deal. 

To  a  great  many  people  the  first  news  of  organised, 
trained  and  scientifically  equipped  rescue  parties  came  at  the 
time  of  the  terrible  Courrieres  disaster  in  France,  when  over 
1000  men  lost  their  lives.  For  then  a  party  with  apparatus 
hurried  from  Germany  and  played  a  prominent  part  in  the 
rescue  operations.  But  unfortunately  the  glamour  of  their 
performance  was  somewhat  dimmed  by  the  fact  that  after 
they  had  done  all  they  could,  and  had  gone  home  again, 
more  men  were  rescued.  Many,  reading  of  that  fact,  were 
inclined  to  scoff  at  the  "  new-fangled  "  ideas,  thinking  that 
after  all  the  old  way  of  working  with  a  party  of  brave  but 
untrained  and  often  ignorant  volunteers  was  better  than  the 
new  way  of  working  with  equipped  and  trained  men.  It 
certainly  did  seem  as  if  the  former  had  succeeded  where 
the  latter  had  failed.  But  that  was  quite  a  mistake,  as 
subsequent  events  have  shown,  and  in  all  probability  it 
was  due  to  the  fact  that  the  uninstructed  party  were  local 
men,  thoroughly  familiar  with  the  mine  in  which  they  were 


222      HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER 

working,   its  geography  and  its  special   local  conditions, 
whereas  the  trained  men  came  from  far  away. 

At  all  events  the  pioneer  work  of  the  Germans  in  the 
matter  of  rescue  teams  has  been  amply  justified  by  the  fact 
that  other  people  have  copied  them,  and  none  more  thor- 
oughly than  the  mining  authorities  of  Great  Britain.  Indeed 
we  see  here  another  instance  of  the  remarkable  way  in  which 
the  British  people,  though  a  little  slow  to  take  up  a  new  idea, 
do  take  it  up  when  it  has  once  been  established,  and  in  such 
a  way  that  they  are  soon  among  the  foremost  in  its  use. 
The  Germans,  all  honour  to  them,  started  the  rescue  teams, 
but  at  this  moment  there  are  rescue  teams  and  stations  for 
their  training  in  Britain  second  to  none  in  the  world.  Of 
these  there  is  a  splendid  example  in  the  Rhondda  Valley,  in 
South  Wales,  supported  and  worked  by  the  owners  of  the 
pits  in  that  district,  besides  others  at  Aberdare,  in  the  same 
neighbourhood,  at  Mansfield,  to  serve  the  collieries  in  Derby- 
shire and  Nottinghamshire  ;  indeed  rescue  stations  are  now 
dotted  throughout  the  mining  districts. 

The  general  idea  of  these  stations  is  as  follows.  The 
building  is  centrally  situated  in  the  district  which  it  is 
intended  to  serve,  and  in  it  are  kept  an  ample  supply  of  the 
necessary  appliances,  in  the  shape  of  breathing  apparatus, 
which  enables  men  to  walk  unhurt  through  poisonous  gas, 
reviving  apparatus,  by  which  partially  suffocated  men  can 
be  brought  round  again  by  the  administration  of  oxygen, 
together  with  quantities  of  that  valuable  gas  in  suitable 
portable  cylinders.  Everything  which  forethought  can 
suggest  as  even  possibly  useful  in  an  emergency  is  kept 
in  a  constant  state  of  readiness.  And  all  the  while  a  swift 
motor  car  stands  ready  to  carry  them  to  the  scene  of 
operations. 

But  the  appliances  are  of  little  use  without  men  to  work 
them,  who  know  them  and  can  trust  them.  The  case  of 
David,  who  felt  able  to  do  better  work  with  his  sling  and 
stone  than  in  all  the  panoply  of  Saul's  armour,  because  he 
"  had  not  proved  it,"  is  typical  of  a  universal  human  instinct. 


HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER      223 

A  man  feels  safer  unarmed,  or  simply  armed,  than  he  does 
with  the  most  elaborate  weapons  in  which  he  has  not  learned 
to  have  confidence.  And  therefore  the  men  who  may  be 
called  upon  to  work  this  apparatus  are  first  taught  to  have 
confidence  in  it.  Each  station  has  its  instructor,  who  is 
usually  also  the  general  superintendent  of  the  station,  and 
"  galleries  "  in  which  the  instruction  can  be  carried  out. 

Volunteers  are  called  for  in  each  colliery  and  a  number  of 
the  most  suitable  men  are  chosen  to  undergo  training,  prefer- 
ence being  given,  very  naturally,  to  those  who  are  already 
trained,  as  fortunately  so  many  workmen  are  nowadays,  in 
ambulance  work. 

These  chosen  men  then  repair  at  intervals  to  the  station 
to  undergo  a  proper  course  of  instruction.  The  instructor, 
often  an  ex-non-commissioned  officer  in  the  Royal  Engineers, 
accustomed,  therefore,  to  engineering  matters,  and  also  to 
systematic  discipline,  there  puts  them  through  a  course  of 
drill  the  object  of  which  is  to  teach  them  to  work  together 
as  a  squad  under  the  orders  of  a  properly  constituted  chief. 
Thus  when  called  upon  in  some  emergency  there  will  be  no 
confusion,  but  each  man  will  know  what  to  do,  and  a  few 
short  words  of  command  from  the  chief  will  serve  better  than 
the  long  explanations  which  would  be  necessary  with  an 
undisciplined  body.  It  welds  the  individual  men,  as  it  were, 
into  a  smoothly  working  machine,  thereby  increasing  the 
efficiency  of  the  whole.  And  arrangements  are  made 
whereby,  should  the  leader  fail,  another  man  steps  into  his 
place  of  authority  at  once  and  without  question. 

Then,  having  thus  brought  them  under  a  suitable  discipline, 
the  instructor  takes  his  men  into  the  experimental  gallery. 
This  may  be  described  as  a  long,  low,  narrow  shed,  in  which 
are  timber  props  and  beams,  rails  on  the  floor,  heaps  of  coal, 
all  things,  in  fact,  which  may  tend  to  make  it  closely  resemble 
the  actual  workings  of  a  coal-mine  after  they  have  been 
shaken  and  shattered  by  the  force  of  an  explosion. 

The  great  difficulty,  in  a  real  disaster,  arises  from  what 
are  known  as  "  falls."  The  roof  of  the  mine  is  normally 


224      HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER 

supported  by  timbers,  and  these  the  explosion  moves,  so 
that  in  places  many  tons  of  the  earth  of  which  the  roof  of 
the  mine  consists  will  fall  and  block  completely  the  "  roads  " 
or  tunnels  which  communicate  from  the  shaft  to  the  places 
where  the  men  are  at  work.  These,  of  course,  have  to  be 
removed  or  burrowed  through  before  the  men  imprisoned 
in  the  distant  workings  can  be  reached.  The  rescue  party 
do  not,  of  course,  wait  to  clear  away  the  whole  of  this 
debris,  only  just  enough  to  enable  them  to  crawl  through 
or  over  it,  but  even  then  it  often  represents  the  waste  of 
precious  hours,  and  the  expenditure  of  great  exertions,  to 
get  past  a  "fall."  So  at  intervals  "falls"  are  made  in 
the  gallery,  in  order  that  men  may  be  practised  in  dealing 
with  them. 

It  may  be  interesting  to  give  a  brief  statement  of  the 
training  undergone  by  the  men  at  the  Mansfield  Rescue 
Station.  In  that  case,  it  should  be  stated,  the  gallery  is  made 
double,  so  that  men  can  go  one  way  and  return  the  other 
back  to  their  starting-point.  Having  donned  their  breathing 
apparatus,  they  enter  the  gallery,  which,  by  the  way,  is  filled 
with  smoke  and  foul  gas.  Passing  along  it,  they  encounter 
two  falls,  which  they  must  get  over  or  through  ;  then  they 
have  to  set  twelve  timber  props  as  might  be  necessary  to 
maintain  the  safety  of  a  damaged  road  in  the  mine ;  all  that 
they  do  three  times  over.  Then  they  are  required  to  bring 
up  and  lay  250  bricks,  a  thing  which  might  also  be  necessary 
in  an  actual  emergency,  after  which  they  have  to  fix  up 
"  brattice  cloth  "  in  a  part  of  the  gallery.  One  of  the  first 
duties,  of  course,  for  a  rescue  party  is  to  restore  the  circula- 
tion of  air  in  the  mine,  and  brattice  cloth  is  a  rough  kind 
of  cloth  which  is  put  to  guide  the  air  currents.  That  done, 
they  have  to  take  a  dummy  representing  a  man  of  14  stone, 
put  it  on  a  stretcher,  and  carry  it  round  the  gallery  and  over 
the  falls.  Finally,  they  restore  the  timber,  bricks  and  cloth, 
and  their  turn  of  work  is  done.  The  total  time  required  for 
this  is  two  hours,  and  during  the  whole  of  that  period  they 
are,  of  course,  breathing  not  the  natural  air,  but  the  artificial 


By permiss-ion  of  II'.  E.  Garforlh,  Esq.,  Ponffract 

AN  ARITFICIAL  COAL  MINE 


These  two  photographs  show  the  clouds  of  flame  and  smoke  issuing  from  the  mouth 
of  the  "Artificial  Coal  Mine"  during  the  experiments  described  in  the  text 


HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER      225 

atmosphere  provided  for  them  by  the  apparatus  with  which 
each  man  is  provided.  The  chief  point  of  this  part  of  the 
training,  as  has  been  remarked  already,  is  to  accustom  the 
men  to  the  wearing  of  the  apparatus  and  to  doing  work  in  it. 
By  this  means  they  gain  confidence  in  it,  and  get  to  know 
that  it  will  not  fail  them  in  the  time  of  trial. 

The  course  of  instruction  consists  of  ten  drills  such  as  has 
been  described,  after  which  the  men  are  called  up  twice  a 
year,  just  to  refresh  their  memories. 

One  side  of  the  gallery  is  glazed,  so  that  the  instructor  can 
watch  his  men  at  work  without  of  necessity  being  inside 
himself,  and  there  are  emergency  doors  as  well,  which  can  be 
opened  to  let  a  man  out  should  the  ordeal  be  too  much  for 
him.  The  necessary  "  fumes "  are  generated  in  a  stove 
and  driven  into  the  gallery  by  a  fan.  The  stations  are 
beautifully  fitted  up,  with  baths  for  the  men  to  wash  after 
their  somewhat  dirty  experience  in  the  gallery,  and  every- 
thing is  done  for  their  convenience  and  welfare. 

The  advantage  of  this  systematic  training  of  a  great 
number  of  men  is  that  there  are  men  at  each  colliery  who 
can  be  called  upon  when  needed.  The  team  of  strangers, 
as  has  been  remarked,  partially  failed  at  Courrieres,  largely 
because  they  were  strangers,  but  when  every  colliery  has  a 
team  ready,  composed  of  its  own  men,  then  clearly  there  is 
the  greatest  chance  of  success.  The  central  station  of  the 
district  is  the  training-ground  where  the  men  go  from  all 
the  collieries  to  get  the  experience  and  instruction,  and 
where  a  reserve  store  of  appliances  is  kept.  In  many  cases, 
of  course,  the  collieries  have  their  own  appliances,  so  that 
work  can  be  begun  at  once,  without  having  to  wait  for  that 
from  the  rescue  station,  but  the  latter  forms  a  reserve  in 
case  of  need,  and,  being  kept  under  the  care  of  an  expert, 
it  is  naturally  always  in  the  best  possible  working  order. 

To  give  an  idea  of  the  cost  of  these  stations,  it  may  be 
stated  that  the  one  at  Forth,  in  the  Rhondda  Valley,  cost, 
including  equipment,  £7000,  while  the  one  at  Mansfield  cost 
£3000.  This  first  cost  and  the  expense  of  maintenance  is 


226      HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER 

borne  by  the  collieries  of  the  district  in  proportion  to  the 
quantity  of  coal  which  they  raise. 

And  now  we  can  turn  to  the  apparatus  itself,  without  which 
the  organisation  already  described  would  be  of  little  value. 

There  are  several  makes  of  these,  but  a  description  of  the 
particular  apparatus  used  at  the  two  stations  mentioned 
will  serve  as  an  illustration.  The  purpose,  of  course,  is  to 
give  the  wearer  an  atmosphere  of  his  own,  which  he  can  carry 
about  with  him,  and  which  will  render  him  quite  indepen- 
dent of  the  ordinary  atmosphere  and  quite  indifferent  to  the 
poisonous  nature  of  the  gases  around  him.  To  this  end  his 
mouth  and  nostrils  must  be  cut  off  from  the  outer  world 
altogether.  There  are  two  ways  of  doing  this.  In  the  one 
there  is  used  a  helmet,  or  perhaps  mask  would  be  the  better 
term.  This  fits  right  over  the  man's  face,  an  air-tight  joint 
being  made  between  the  helmet  and  his  head  by  means  of  a 
rubber  washer  which  can  be  inflated  with  air.  The  inflation 
is  accomplished  by  squeezing  a  rubber  ball  on  the  right- 
hand  side  of  the  helmet.  In  the  centre  is  a  glass  window 
through  which  he  can  see  easily,  and  since  this  is  apt  to 
become  clouded  by  the  dampness  of  his  breath  there  is  a 
wiper  inside,  which  can  be  turned  by  a  knob  on  the  outside, 
so  that  by  simply  turning  his  knob  with  his  hand  he  can 
clean  the  window  at  any  time  that  may  be  necessary. 
Two  soft  pads  inside  the  helmet  bear  one  on  the  man's 
forehead  and  the  other  on  his  chin,  and  these,  working  in 
conjunction  with  a  strap  which  passes  right  round  the  back 
of  his  head,  keep  the  thing  firmly  in  position.  In  addition 
there  is  combined  with  the  helmet  a  leather  skull-cap  which, 
being  continued  down  behind,  gives  good  protection  to  the 
head  and  neck. 

The  other  form  of  apparatus  consists  of  a  mouth-piece  and 
nose-clip.  The  mouth-piece,  as  its  name  implies,  fits  in  the 
man's  mouth,  being  supported  and  kept  in  position  by  a 
strap  passing  behind  the  back  of  his  head.  Combined  with 
it  is  a  little  screw  clip  which  closes  his  nostrils.  The  man 
also  wears  a  leather  skull-cap,  from  which  straps  depend  to 


HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER      237 

bear  the  weight  of  the  mouth-piece  and  its  attached  tubes,  so 
that  the  weight  does  not  fall  upon  his  mouth. 

Either  of  these  arrangements,  it  is  clear,  cuts  him  off  from 
communication  with  the  outer  air,  but  that  is  only  half  the 
problem,  for  he  must  be  given  a  substitute  or  he  will  be 
suffocated. 

This  part  of  the  appliance  he  carries,  knapsack  fashion, 
upon  his  back.  First  there  is  a  rectangular  case,  called  the 
regenerator,  with,  below  it,  two  small  cylinders  of  com- 
pressed oxygen.  A  suitable  arrangement  of  pipes  connects 
these  together,  and  to  the  helmet  or  mouth-piece  as  the  case 
may  be. 

When  the  man  exhales,  as  we  all  know,  the  air  which  he 
then  discharges  from  his  lungs  is  deficient  in  oxygen  and 
instead  contains  carbonic  acid  gas.    The  latter  must  be  got 
rid  of  and  replaced  by  pure  oxygen.    The  exhaled  air  is 
therefore  led  down  a  pipe  to  the  regenerator,  where  it  comes 
into  contact  with  several  trays  of  caustic  soda,  a  chemical 
which  has  a  great  affinity  for  carbonic  acid.    The  result  is 
that  the  latter  gas  is  extracted  from  the  impure  air,  finding  a 
more  congenial  home  in  the  caustic  soda.   It  is  then  necessary 
to  restore  the  normal  quantity  of  oxygen,  and  so,  as  the  air 
passes  on,  it  meets,  in  a  little  apparatus  known  as  an  injector, 
a  spray  of  pure  oxygen  from  the  cylinders.    Thus,  after 
being  purified  and  re-oxygenated,  the  air  passes  on  through 
more  pipes  to  the  helmet  or  mouth-piece,  to  be  breathed 
once  more.    The  apparatus  contains  sufficient  oxygen  and 
caustic  soda  for  this  to  go  on  for  a  space  of  two  hours. 
But  during  times  of  extra  exertion  a  man  needs  more  air 
than  at  others,  for  which  provision  has  to  be  made,  and  so 
on  his  chest  the  rescuer  carries  a  flexible  bag  divided  into 
two  compartments.    Through  one  of  these  the  exhaled  air 
passes  on  its  way  to  the  regenerator,  while  through  the  other 
the  oxygenated  air  flows  on  its  way  to  the  man's  mouth. 
When  he  is  breathing  hard,  then,  during  a  moment  of  extra 
exertion,  and  when,  therefore,  he  is  turning  out  bad  air 
faster  than  it  can  be  purified,  and  drawing  in  pure  air  faster 


228      HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER 

than  it  can  be  produced,  this  bag  comes  to  his  aid.  From 
the  store  of  oxygenated  air  in  one  side  of  it  he  draws  the 
extra  which  he  requires,  while  the  other  side  stores  up 
temporarily  the  excess  of  vitiated  air,  until  the  regenerator 
is  able  to  overtake  its  work.  Thus  at  all  times,  whether 
breathing  ordinarily  or  heavily,  the  apparatus  can  respond 
to  his  demands. 

The  spray  of  oxygen  as  it  escapes  from  the  cylinders  into 
the  injector  has  the  effect  of  driving  the  air  along,  so  that 
the  circulation  through  the  tubes  and  the  regenerator  is 
automatic,  and  the  foul  air  flows  away  from  the  man's 
mouth  and  the  new  air  comes  back  to  him  quite  without 
effort  on  his  part.  As  time  goes  on,  of  course,  and  the 
stored  oxygen  becomes  used  up,  the  pressure  in  the  cylinders 
falls,  which  fall,  shown  upon  a  little  pressure-gauge,  tells 
the  man  how  much  longer  time  he  has  before  he  must  return 
for  fresh  supplies  of  oxygen  and  soda.  Fresh  cylinders  of 
oxygen  can  be  connected  up  very  quickly  in  place  of  the 
empty  ones,  while  a  fresh  regenerator  can  be  put  in,  or  new 
caustic  soda  supplied,  in  a  very  short  time. 

The  superintendent  of  the  Mansfield  station  has  invented 
what  is  termed  a  "  self -rescue  "  apparatus,  to  be  used  in 
conjunction  with  that  which  has  been  described  above.  It 
is  simpler  and  lighter  than  the  rescue  apparatus,  and  will 
not  keep  a  man  supplied  with  air  for  more  than  an  hour  or 
an  hour  and  a  quarter.  Moreover,  it  is  not  automatic,  since 
the  flow  of  oxygen  has  to  be  controlled  by  the  man  himself. 
Since,  however,  it  consists  only  of  a  mouth-piece,  a  breathing - 
bag  and  a  cylinder  of  oxygen,  it  is  very  portable,  and  may 
well  be  carried  by  a  rescue  party  for  the  use  of  any  men  who 
may  be  discovered  alive  beyond  the  danger  zone.  It  may 
well  happen,  indeed  it  often  has  happened,  that  a  remote 
part  of  a  mine,  although  cut  off  from  the  shaft  by  passages 
full  of  "  afterdamp,"  as  the  foul  gases  caused  by  the  explosion 
are  termed,  may  itself  contain  fairly  pure  air  in  which  men 
can  live  for  a  long  time.  If  such  men  be  reached,  the 
difficulty  is  to  get  them  through  the  passages  containing  the 


HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER      229 

bad  air.  Consequently  a  rescue  party  which  carried  one  or 
two  of  these  light  forms  of  apparatus  could  equip  such  men 
with  them  and  then  they  could  pass  out  with  safety. 

Another  use,  the  one,  in  fact,  from  which  the  appliance 
draws  its  name,  is  the  facility  with  which,  by  its  aid,  a  man 
could  set  right  a  chance  defect  in  his  ordinary  rescue  ap- 
paratus. Suppose,  for  example,  that  a  fully  equipped  man 
found  something  wrong,  whereby  he  was  prevented  from 
getting  his  proper  supply  of  purified  air.  Then,  if  the  party 
had  one  of  the  self-rescue  sets  with  them,  he  could  slip  off 
his  helmet  or  mouth-piece,  quickly  replacing  it,  for  a  time, 
with  the  self-rescue  mouth-piece.  This  might  enable  him 
to  reach  safety,  or  even  to  put  the  other  apparatus  right  and 
then  don  it  once  more.  The  whole  thing  can  be  packed 
up  into  a  small  tin  case  which  can  be  slung  over  one  shoulder, 
and  with  the  oxygen  cylinder  slung  over  the  other  one  the 
complete  outfit  can  be  carried  quite  easily  by  a  man  in 
addition  to  what  he  is  wearing  himself. 

Still  another  form  of  breathing  appliance  may  well  be 
taken  on  these  rescue  expeditions,  and  that  is  the  reviving 
apparatus,  for  use  upon  those  who  have  apparently  ceased 
to  breathe.  In  this  case  a  mask  is  put  over  the  sufferers' 
mouth  and  nose,  and  then  the  turning  of  a  lever  into  a  certain 
position  causes  oxygen  to  escape  from  a  cylinder  in  such  a 
way  as  to  cause  a  suction  which  empties  the  man's  lungs 
of  the  bad  gases  which  have  laid  him  low.  That  done, 
another  movement  of  the  lever  and  a  deep  breath  of  oxygen 
flows  into  his  lungs  in  their  place.  Thus  by  alternating 
the  positions  of  the  lever  an  artificial  respiration  is  set  up 
far  more  effective  than  can  possibly  be  attained  by  the 
ordinary  method  of  moving  the  man's  arms  and  pressing  his 
chest.  Indeed  there  are  cases,  such  as  when  his  arms  or 
ribs  are  injured,  when  the  ordinary  method  is  impossible, 
but  it  is  hard  to  imagine  an  instance  when  this  beneficent 
apparatus  could  not  be  used,  and  so  long  as  there  be  any 
spark  of  life  left  in  the  poor  fellow  there  seems  to  be  every 
reason  to  expect  a  complete  revival  as  the  result  of  its  use. 


280      HOW  SCIENCE  AIDS  THE  STRICKEN  COLLIER 

Of  course  there  are  many  other  places  where  poisonous 
gases  are  likely  to  be  met  with,  such  as  gasworks,  chemical  - 
works,  limeworks,  and  so  on,  where  this  apparatus  may  be 
kept  with  advantage,  in  case  of  accident. 

Indeed  all  that  has  been  described  above  has  its  use 
apart  from  colliery  explosions,  although  they  are  the  out- 
standing opportunities  for  its  employment.  Old  workings, 
tunnels  which  have  been  empty  for  a  time,  sewers — all  these 
have,  on  occasion,  to  be  entered,  not  to  mention  houses  full 
of  smoke,  or  factories  full  of  chemical  fumes,  all  of  which 
form  cases  in  which  the  rescue  apparatus  would  find  useful 
employment. 


CHAPTER  XIX 

HOW  SCIENCE  HELPS   TO  KEEP  US  WELL 

ONE  branch  of  science — medical  science — concerns 
itself  almost  entirely  with  health,  but  it  would  be 
out  of  place  to  refer  to  such  matters  here,  even  if 
the  present  writer  were  capable  of  doing  justice  to  the 
subject.  A  new  medicine  or  a  new  method  of  operating 
upon  a  suffering  patient  would  be  quite  correctly  described 
as  a  scientific  marvel,  but  it  is  not  of  such  that  this 
chapter  deals,  but  rather. with  those  great  works  by  which 
the  engineer,  often  taught  by  the  medical  man,  promotes 
the  health  of  a  whole  community. 

Most  important  of  these,  perhaps,  is  the  provision  of  pure 
water.  Some  places  are  more  fortunately  situated  than 
others  in  this  respect,  being  near  streams  flowing  down  from 
mountains  clear  and  unpolluted,  which  can  be  drunk  after 
the  minimum  of  purification.  Others  have  to  make  use  of 
the  waters  of  a  moderately  clean  river,  as  London  does  those 
of  the  Thames  and  Lea,  in  which  cases  the  greatest  care  has 
to  be  exercised  in  the  nitration  of  the  liquid  before  it  can  be 
sent  out  through  the  mains  for  domestic  consumption. 

In  this  particular  domain  invention  has  been  compara- 
tively slow.  There  are  novel  pumps,  it  is  true,  for  handling 
the  water,  such  as  the  Humphrey  Gas  Pump,  which  the 
Metropolitan  Water  Board  (London)  have  installed  for  filling 
their  great  reservoirs  at  Chingford.  In  these  an  explosion 
of  gas  is  the  motive  force.  Water  flows  by  gravitation  into 
a  huge  iron  pipe  closed  at  the  top  but  open  at  the  bottom. 
It  is  so  arranged  that  a  quantity  of  gas  shall  be  entrapped 
in  the  upper  end,  which,  being  exploded  by  an  electric 
spark,  drives  the  mass  of  water  out.  Some  of  it,  together 
231 


282     HOW  SCIENCE  HELPS  TO  KEEP  US  WELL 

with  a  quantity  of  fresh  water,  presently  comes  surging 
back,  entrapping  a  fresh  supply  of  gas  and  causing  a  new 
explosion ;  and  so  it  goes  on  over  and  over  again.  The 
particular  pumps  at  the  waterworks  referred  to  discharge 
about  fourteen  tons  of  water  at  each  explosion,  of  which 
there  are  nine  every  minute. 

The  special  effect  of  these  machines,  however,  is  not  to 
improve  the  public  health  so  much  as  to  relieve  the  public 
pocket,  for  their  chief  feature  is  that  they  work  more 
economically  than  any  other  kind  of  pump. 

The  filters,  by  which  the  water  is  purified,  are  simply 
layers  of  sand,  much  the  same  as  have  been  in  use  for  many 
years,  although  in  some  cases  chemistry  is  brought  in  and 
the  work  of  the  filters  aided  by  the  action  of  precipitants. 
These  are  substances  which  combine  in  some  way  with  the 
impurities  in  the  water,  and  carry  them  to  the  bottom  of 
the  tank  or  reservoir,  while  the  pure  water  remains  to  be 
drawn  off  from  the  top. 

This  is  also  the  most  usual  method  by  which  water  is 
softened.  Hardness  in  water  is  due  to  the  presence  of 
certain  salts  which  are  dissolved  out  of  the  ground  as  the 
water  percolates  through  it,  and  which  are  absent  from 
rain-water.  To  get  rid  of  these  the  hard  water  has  chemicals 
mixed  with  it  in  a  tank,  from  which  it  flows  slowly  through 
another  tank.  The  effect  of  the  added  chemicals  is  to 
convert  the  soluble  salts  in  the  water  into  insoluble 
particles,  which  then  tend  to  fall  down  to  the  bottom 
of  the  containing  vessel.  The  slow  passage  through  the 
second  tank  is  intended  to  give  the  particles  time  to  settle. 

Finally,  to  make  sure  that  these  have  been  all  got  rid 
of,  the  water  traverses  a  filter,  and  then  it  is  for  all  practical 
purposes  as  soft  as  rain-water.  Some  people  are  frightened 
of  this  artificially  softened  water,  on  the  ground  that  chemicals 
have  been  added  to  it,  supposing,  apparently,  that  when 
they  use  such  water  they  are  really  employing  a  chemical 
solution.  That  is  quite  wrong,  however,  for  the  added 
chemicals,  combining  with  the  "hardness,"  form  substances 


HOW  SCIENCE  HELPS  TO  KEEP  US  WELL     283 

which  are  quite  easily  extracted  from  the  water  altogether. 
If  we  liken  the  hardness  to  a  number  of  pickpockets  in  a 
crowd,  and  the  added  chemicals  to  a  number  of  policemen 
who  come  in  to  arrest  the  said  pickpockets,  finally  leaving 
the  crowd  free  from  both  pickpockets  and  policemen,  we 
get  a  simple  illustration  of  what  takes  place. 

But  almost  equally  important  as  the  provision  of  pure 
water  is  the  effective  dealing  with  the  drainage  of  a  large 
town.  Much  offensive  matter  flows  under  the  streets  of 
our  towns  and  cities,  and  if  it  is  not  to  become  a  nuisance 
it  must  be  scientifically  dealt  with. 

Years  ago  the  drains  of  London  simply  emptied  them- 
selves into  the  Thames,  until,  in  1864,  two  large  drains  were 
constructed,  one  on  each  side  of,  and  approximately  parallel 
with,  the  river,  to  intercept  the  old  drains  and  to  carry  their 
contents  to  points  many  miles  down  towards  the  sea.  Even 
that,  however,  by  no  means  abated  the  evil,  for  it  simply 
transferred  it  to  a  new  place.  The  river  was  as  foul  as  ever. 

William  Morris,  in  News  from  Nowhere,  pictures  the  catch- 
ing of  salmon  in  the  Thames  off  Chelsea,  while  one  of  London's 
prominent  citizens,  referring  to  what  was  being  done  in  the 
direction  of  purifying  the  river,  jocosely  promised  the 
members  of  Parliament  a  little  fly-fishing  at  Westminster. 
Equally  remote,  it  is  to  be  feared,  from  actual  accomplish- 
ment, these  two  prophecies  do  certainly  indicate  the  ten- 
dency of  events,  for  science  has  enabled  the  authorities  to 
relieve  the  long-suffering  river  of  much  of  the  pollution 
which  they  used  to  thrust  into  it. 

The  first  great  step  was  the  introduction,  in  1887,  of  a 
treatment  in  principle  very  like  that  just  described  for 
softening  water.  The  liquid  from  the  drains  is  gathered  into 
large  reservoirs,  where  chemicals  are  added  to  it,  causing  the 
heavier  matter  to  be  precipitated  in  the  form  known  as 
"  sludge." 

The  liquid  portion,  or  "  effluent,"  as  it  is  called,  which  is 
left  is  discharged  into  the  river  just  as  the  tide  is  ebbing, 
so  that  it  is  carried  right  away,  and,  being  comparatively 


284     HOW  SCIENCE  HELPS  TO  KEEP  US  WELL 

inoffensive,  it  pollutes  the  river  very  little  indeed.  The 
sludge,  on  the  other  hand,  is  pumped  into  special  steamers, 
which  carry  it  down  to  a  certain  spot  off  the  Thames  Estuary, 
where  they  drop  it  into  the  sea.  The  currents  at  the  par- 
ticular spot  chosen  are  such  that  none  of  it  returns  to  the 
river. 

For  a  similar  purpose  electrolysis  has  been  employed.  In 
this  process  the  sewage  is  made  to  flow  between  two  iron 
plates  which  are  connected  up  to  a  source  of  electric  current 
so  that  they  form  electrodes,  while  the  sewage  is  the  electro- 
lyte. The  current  decomposes  the  liquid  sewage,  causing 
chlorine  and  oxygen  to  be  deposited  upon  that  plate  which 
forms  the  anode.  This  deodorises  and  purifies  the  sewage, 
in  addition  to  which  iron  salts  are  formed  on  the  iron  plates, 
the  effect  of  which  is  to  precipitate  the  solid  particles.  Thus 
the  same  result  is  achieved  as  when  chemicals  are  used,  the 
main  difference  being  that  instead  of  chemicals  being  added, 
they  are  produced  by  the  passage  of  the  current. 

But,  from  the  scientific  point  of  view,  the  most  interesting 
process  of  all  is  that  in  which  bacteria  or  microbes  are  brought 
into  the  service.  The  fact  is  familiar  to  most  people  that 
there  are  certain  minute  organisms  which  cause  terrible 
diseases.  It  is  not  so  well  known  that  there  are  still  more 
of  them  whose  action  is  extremely  beneficent.  The  writer 
has  seen  these  minute  living  things  described  in  a  popular 
book  as  "  insects,"  but  they  really  belong  to  a  low  order  of 
plant  life,  and,  as  has  been  said  in  an  earlier  chapter,  in  spite 
of  the  lowliness  of  their  status  in  the  order  of  creation,  they 
are  able  to  accomplish  certain  chemical  processes  which 
baffle  the  cleverest  men.  They  are  particularly  good,  or 
some  of  them  are  at  any  rate,  at  forming  compounds  in  which 
nitrogen  forms  a  part.  Further,  they  can  be  divided  into 
two  classes,  the  aerobic  and  the  anaerobic.  The  former 
work  best  in  air,  while  the  latter  need  an  absence  of  air 
while  they  perform  their  functions.  After  which  pre- 
liminary explanation  we  can  proceed  to  describe  how  they 
are  induced  to  carry  on  this  valuable  work  for  mankind. 


HOW  SCIENCE  HELPS  TO  KEEP  US  WELL     285 

The  sewage  flows  first  of  all  into  a  tank  from  which  light 
and  air  are  excluded  as  far  as  possible.  There  the  anaerobic 
microbes  flourish  and  multiply,  and  in  the  course  of  their 
life  work  they  convert  the  sewage  into  an  inoffensive  liquid. 
After  an  appropriate  interval  the  liquid  passes  to  filter-beds, 
where  it  trickles  over  and  through  beds  of  coke,  the  effect  of 
which  is  to  aerate  it  very  thoroughly,  whereby  the  aerobic 
microbes  come  into  action,  completing  the  good  work,  so 
that  nothing  is  left  except  a  clean,  colourless  and  odourless 
liquid.  Indeed  it  is  more  than  that,  for  the  microbes  have 
turned  the  offensive  matter  into  nitrogenous  compounds 
which,  as  we  have  seen  in  a  previous  chapter,  are  the  best 
fertilisers.  Hence  this  effluent,  if  placed  upon  the  soil,  is 
of  great  value. 

The  advantage  of  this  to  towns  which  are  not  blessed,  like 
London,  with  a  broad  river  and  the  sea  near  at  hand  needs 
no  explanation. 

The  bacteria  necessary  to  carry  on  the  process  are  always 
present  in  sewage,  and  after  any  particular  plant  has  been  in 
operation  for  a  little  while  there  results  an  accumulation  of 
them,  so  that  the  process  becomes  more  and  more  active  as 
time  goes  on.  Mechanical  ingenuity  has  so  arranged  matters 
that  a  sewage  disposal  plant  on  this  system  can  be  made 
quite  automatic,  requiring  little  or  no  attention  for  months 
together,  the  raw  sewage  flowing  in  at  one  end,  while  the 
odourless,  harmless  effluent  pours  out  at  the  other. 

And,  moreover,  so  powerful  is  the  action  of  these  beneficent 
bacteria  that  should  disease  germs  come  down  in  the  sewage 
they  soon  destroy  them.  No  chemicals  are  needed,  for  the 
bacteria  replenish  themselves.  No  sludge  is  left,  everything 
being  turned  into  the  harmless  effluent.  And,  it  may  be 
said  once  more,  disease  germs  are  destroyed.  Of  all  the 
valuable  inventions  of  modern  times  this  is  surely  not  one 
of  the  least. 


CHAPTER  XIX 

MODERN   ARTILLERY 

EVEN  as  late  as  the  time  of  the  Crimean  War  guns, 
even  the  largest,  were  made  of  that  extremely 
common  material,  cast-iron.  In  fact,  so  far  as 
material  went,  there  was  no  difference  between  a  gun  and  a 
water-pipe. 

It  was  the  need  for  some  material  possessing  strength 
comparable  with  that  of  steel  combined  with  the  ease  of 
production  of  cast-iron  which  led  Sir  Henry  Bessemer  to 
experiment  in  the  manufacture  of  steel.  Out  of  those 
experiments  came  Bessemer  steel  and  its  near  relative, 
Siemens  steel,  two  materials  of  universal  application  at  the 
present  time,  so  that  to  the  needs  of  the  artilleryman  we 
owe  two  inventions  which  have  proved  of  infinite  value  in 
peace  as  well  as  in  war. 

If  any  particular  piece  of  ordnance  can  be  said  to  be  the 
prime  favourite  with  the  English-speaking  peoples,  it  is  the 
big  naval  gun.  With  both  British  and  Americans  the  navy 
takes  pride  of  place  ;  both  nations  are  given  to  contemplat- 
ing with  pleasure  the  number  of  dreadnoughts  which  they 
possess,  and  the  distinguishing  feature  of  a  dreadnought 
is  the  large  number  of  big  guns  which  it  carries. 

Of  the  latest  of  these  gigantic  weapons  one  may  not  speak, 
but  much  is  already  public  property  concerning  the  12-inch 
gun  which  the  original  Dreadnought  carried,  and  whch  is 
probably  followed  in  its  general  features  by  the  still  greater 
guns  of  the  most  recent  ships. 

A  gun  is  spoken  of  by  its  "calibre,"  which  means  the 
inside  diameter,  or,  to  use  another  expression,  the  size  of 
the  "  bore."  So  the  "  12-inch  "  naval  gun  is  12  inches  in  the 

236 


MODERN  ARTILLERY  237 

bore.  Its  length  is  in  some  cases  45  calibres  and  in  others 
50  calibres.  In  other  words,  some  are  45  feet  long  and  others 
50  feet. 

Why  the  difference  ?  someone  may  ask.  The  answer  is 
that  the  longer  ones  are  an  improved  type.  The  extra 
length  gives  longer  range  and  harder  hits,  as  is  quite  apparent 
after  a  little  thought.  The  explosive  "  goes  off  "  and  forth- 
with commences  to  drive  the  shell  towards  the  muzzle. 
So  long  as  it  is  in  the  gun  the  shell  is  being  pushed  faster 
and  faster,  but  so  soon  as  it  leaves  the  muzzle  the  pushing 
ceases  and  the  shell  is  left  to  pursue  its  course  with  its  own 
momentum.  Therefore,  generally  speaking,  one  may  say 
that  the  longer  the  gun  the  faster  will  be  the  speed  of  the 
shell  as  it  leaves  the  muzzle,  the  farther  will  it  go  and  the 
harder  will  be  the  blow  at  a  given  range. 

Incidentally  this  explanation  reveals  the  need  for  different 
kinds  of  explosive.  The  propellant  whose  function  it  is  to 
drive  the  shell  out  of  the  gun  is  different  from  that  with 
which  the  shell  is  itself  filled.  The  former  needs  to  act  com- 
paratively slowly,  so  that  it  may  continue  its  pushing  action 
during  the  whole  time  that  the  shell  is  travelling  along  the 
gun.  It  might  be  ever  so  powerful,  but  were  its  action  too 
sudden  it  would  simply  tend  to  burst  the  gun,  without 
imparting  very  much  speed  to  the  shell.  On  arrival  at  its 
destination,  however,  the  shell  needs  to  burst  suddenly  and 
violently. 

Another  interesting  question  arises  at  this  point.  Seeing 
how  fast  is  even  the  slowest  speed  at  which  a  projectile 
travels,  how  can  it  be  possible  to  measure  the  rate  at  which 
a  shell  issues  from  one  of  these  monster  guns.  Needless 
to  say,  it  is  electricity  which  makes  a  thing  apparently  so 
difficult  really  quite  easy. 

Near  the  gun  is  set  up  a  frame  with  a  wire  zigzagging  to 
and  fro  across  it,  in  such  a  manner  that  when  the  gun  is 
fired  the  shell  is  bound  to  cut  the  wire.  Electric  current 
is  made  to  pass  through  this  wire  on  its  way  to  a  suitable 
house  in  which  are  recording  instruments,  where  it  energises 


288  MODERN    ARTILLERY 

a  magnet  and  so  holds  something  up.  Now  it  is  easy  to  see 
that  as  soon  as  the  shell  cuts  the  wire  the  current  will  stop, 
the  magnet  will  "  let  go  "  and  the  "  something  "  will  drop. 
At  a  certain  distance  farther  on  there  is  a  second  frame 
with  wires  upon  it,  through  which  passes  a  second  current, 
which  is  also  led  to  the  instrument  house,  where  it  again 
operates  a  second  magnet. 

When  the  first  magnet  releases  its  hold  it  drops  something, 
to  wit,  a  long  lead  weight.  When  the  second  magnet  lets  go 
it  permits  a  second  weight  to  fall  against  the  first  and  make 
a  dent  or  scratch  upon  it.  The  longer  the  interval  between 
the  action  of  the  two  magnets  the  higher  up  upon  the  lead 
weight  will  the  scratch  be.  The  apparatus,  in  short,  will 
register  the  distance  fallen  through  by  the  lead  weight 
between  the  breaking  of  the  wire  in  the  first  frame  and  the 
breaking  of  the  wire  in  the  second  frame. 

Now  a  falling  object,  if  only  it  has  such  weight  that  the 
resistance  of  the  air  is  negligible,  falls  according  to  a  well- 
understood  law,  which  law  it  obeys  with  the  utmost  accuracy. 
Therefore  the  distance  fallen  by  the  weight  between  the 
passage  of  the  shell  through  two  points  gives  a  very  accurate 
record  of  the  time  taken  to  travel  from  one  to  the  other. 
Of  course  several  such  frames  can  be  used  if  desired  in  the 
same  way. 

But  to  return  to  the  gun  itself.  It  is  not  merely  one  piece 
of  metal  but  several  tubes  beautifully  fitted  one  inside 
another.  Moreover,  in  the  British  gun  at  all  events,  between 
two  of  the  tubes  there  is  a  space  filled  with  "  wire." 

This  wire  is  perhaps  better  described  as  steel  tape,  and  is 
of  the  finest  material  for  the  purpose,  flexible  and  tremend- 
ously strong.  It  is  wound  round  and  round  one  of  the  tubes 
until  there  are  many  miles  of  it  on  a  single  gun.  It  is  wound 
tightly,  too,  by  means  of  special  machinery. 

The  purpose  of  the  wire  is  to  resist  cracking.  The  solid 
steel  tubes  may  crack,  and,  as  is  the  way  with  all  cracks,  these 
will  tend  to  grow  longer  and  longer.  The  many  turns  of 
wire,  however,  will  not  crack.  Even  if  a  few  turns  should 


MODERN  ARTILLERY  289 

break,  the  damage  will  not  spread,  and  the  gun  can  probably 
go  on  as  if  nothing  had  happened. 

The  material  of  which  these  guns  are  made  is  nickel 
chrome  gun  steel.  Steel  is  ordinarily  an  alloy  of  iron  and 
carbon,  but  this  metal  also  contains  traces  of  nickel  and 
chromium,  which  make  it  specially  suitable  for  its  special 
purpose. 

Each  of  the  tubes  of  which  the  gun  is  formed  start  as  an 
ingot,  a  mere  lump  of  metal,  but  roughly  shaped.  The 
requisite  mixture  is  obtained  in  a  furnace  and  the  molten 
metal  is  run  out  into  a  mould.  The  ingot  is  heated  again 
and  pressed  under  enormous  hydraulic  presses  until  it  is 
approximately  the  shape  required.  This  pressing  not  only 
produces  the  desired  shape,  it  also  improves  the  quality  of 
the  metal. 

The  rough  forging  is  then  bored  out,  to  make  it  into  a 
tube.  One  is  inclined  to  wonder  why  the  ingot  is  not  cast 
hollow  to  commence  with,  and  so  save  the  labour  of  boring 
it  all  out  later.  The  explanation  of  this  is  that  certain 
impurities  are  always  present  in  the  metal  and  these  always 
gather  together  in  the  part  which  sets  last.  Now  in  a  solid 
block  or  ingot  it  is  clear  that  the  centre  is  the  part  which 
will  set  last,  and  hence  that  is  the  part  where  the  impurities 
will  congregate.  Then,  when  the  centre  part  is  all  bored 
out  the  impurities  are  entirely  removed. 

The  tube  is  shaped  externally  by  being  turned  in  a  lathe. 

The  innermost  tube  is  not  simply  smooth.  There  is  a 
spiral  groove,  called  the  "  rifling,"  running  round  and  round, 
screw  fashion,  inside  it.  The  purpose  of  this  is  to  give  the 
shell  a  spinning  action  which  causes  it  to  keep  point  fore- 
most throughout  its  flight.  But  for  this  the  shell  would 
tend  to  turn  over  and  over,  resulting  in  uncertain  and 
inaccurate  flight. 

The  shell  is  a  little  smaller  than  the  bore  of  the  gun,  but 
near  its  base  it  has  an  encircling  band  of  soft  copper,  which 
band  is  a  tight  fit  in  the  gun.  The  soft  copper  crushes  into 
the  "  rifiing,"  whereby  the  shell  obtains  its  spinning  action. 


240  MODERN  ARTILLERY 

The  large  guns  are  mounted  in  pairs,  each  pair  on  a  turn- 
table, by  the  movement  of  which  to  right  or  left  they  are 
trained  upon  the  distant  target.  The  turntable  is  sur- 
rounded by  a  wall  of  thick  armour  and  is  covered  by  an 
iron  hood  or  roof. 

In  addition  to  being  turnable  to  right  or  left,  there  is,  of 
course,  provision  for  raising  or  depressing  the  direction  in 
which  each  gun  is  pointing.  They  need  always  to  point 
more  or  less  upwards,  and  the  particular  angle  depends 
upon  the  range  or  distance  of  the  object  aimed  at.  This  is 
ascertained  by  range -finding  instruments  and  communicated 
to  the  officers  in  the  turrets,  as  the  covered  turntables  are 
called.  The  guns  are  then  elevated  or  depressed  to  suit  the 
range. 

Each  gun  rests  upon  a  cradle  which  is  itself  fitted  upon  a 
slide.  When  it  is  fired  it  "kicks"  backwards,  against  the 
force  of  a  buffer  of  springs,  or  a  hydraulic  or  pneumatic 
cylinder.  Thus  after  each  shot  the  gun  moves  backwards 
upon  the  slide,  but  the  hydraulic  apparatus  brings  it  back 
again  into  position  for  firing  almost  instantaneously. 

In  naval  guns  all  the  movements,  including  that  of  the 
turntable,  are  by  power,  either  hydraulic  or  electric,  or  a 
combination  of  the  two.  The  loading  is  also  by  power. 

The  shells  and  ammunition  are  kept  well  down  towards 
the  bottom  of  the  ship,  under  each  turret.  Lifts  bring  them 
up  from  there  to  a  chamber  just  beneath  the  turntable, 
known  as  the  working  chamber.  Here  a  small  quantity 
only  is  kept,  and  that  for  as  short  a  time  as  possible  before 
it  is  sent  up  by  other  hoists  straight  to  the  guns  themselves. 
The  hoists  are  so  arranged  that,  no  matter  how  they  may  be 
elevated  or  depressed,  the  ammunition  is  delivered  exactly 
opposite  the  breech,  as  the  rear  end  of  a  gun  is  termed. 
Then  a  mechanical  rammer  pushes  it  straight  in. 

The  breech  of  the  gun  is  closed  by  a  beautiful  piece  of 
mechanism  called  the  breech-block.  It  is  really  a  huge 
plug  which  securely  closes  the  end  of  the  gun,  a  partial 
turn  after  it  is  in  place  fixing  it  firmly  enough  to  resist  all 


RIFLES  OF  DIFFERENT  NATIONS 


(See  Appendix) 


MODERN  ARTILLERY  241 

the  force  of  the  explosion.  Yet  it  can  be  freed  and  swung 
back  upon  hinges  in  a  few  seconds.  At  the  same  moment 
that  it  is  opened  a  jet  of  air  blows  into  the  gun,  clearing  out 
all  effects  of  the  recent  explosion. 

The  process  of  firing  one  of  these  guns  may  thus  be  sum- 
marised. The  turntable  is  swivelled  to  right  or  left  until 
the  gunners,  looking  through  the  sights,  which  are  really 
telescopes,  see  the  object  straight  in  front  of  them.  Mean- 
while the  sights  have  been  set  according  to  the  range — that 
is  to  say,  they  have  been  so  set  in  relation  to  the  gun  itself 
that  when  they  point  directly  at  the  target  the  gun  will  be 
pointed  upwards  at  exactly  the  right  angle  for  that  range. 
The  whole  thing,  therefore,  gun  and  sights  combined,  is 
tilted  upwards  or  downwards  as  may  be  necessary  until  the 
sights  point  directly  at  the  object  aimed  at.  Then  at  a 
signal  the  gun  is  fired  by  electricity.  The  shock  causes  the 
gun  to  slide  backwards  upon  its  supporting  slide,  but  the 
buffers,  having  taken  the  shock  automatically,  return  it  to 
its  position  again ;  the  aim  is  thus  undisturbed  and  it  is 
ready  for  the  next  shot.  These  enormous  guns  can  be 
fired  at  the  rate  of  one  shot  every  fifteen  seconds. 

Field  guns  are  in  principle  very  similar  to  these,  only,  of 
course,  they  are  much  smaller  and  are  mounted  upon  carriages, 
so  that  they  can  be  quickly  moved  from  place  to  place.  It 
must  be  borne  in  mind,  however,  that  there  are  in  the  case 
of  land  guns  two  distinct  types.  Field  guns,  like  naval  guns, 
fire  straight  at  their  target ;  howitzers  or  mortars  fire 
upwards  with  a  view  to  letting  the  shell  fall  on  the  target 
from  above.  The  latter  are,  generally  speaking,  short,  fat, 
stumpy  guns,  as  compared  with  the  long,  slender  field  guns. 

In  the  field  all  guns  have  to  be  loaded  by  hand.  The 
elaborate  system  of  hoists  which  enables  the  great  naval  guns 
to  be  loaded  with  such  rapidity  is  obviously  impossible. 
That  has  to  be  compensated  for  by  the  skill  and  quickness 
of  the  gunners  themselves,  and  it  is  indeed  astonishing  to 
see  with  what  deftness  they  can  handle  the  heavy  and 
dangerous  projectiles. 


242  MODERN  ARTILLERY 

With  all  guns,  of  whatever  kind,  range-finding  is  of  the 
utmost  importance.  No  projectile,  however  fast  it  may 
travel,  really  moves  in  a  straight  line.  It  must  be  fired 
more  or  less  upwards  in  order  to  compensate  for  the  down- 
ward pull  of  gravity.  If  the  elevation  be  insufficient  the 
shell  will  fall  short ;  if  it  be  too  much  it  may  go  beyond 
the  mark,  or  it  may  fall  short,  according  to  circumstances. 
Just  the  right  elevation  is  absolutely  essential  for  good 
shooting.  And  for  that  to  be  achieved  the  range  must  be 
known  with  the  utmost  possible  accuracy. 

There  are  various  systems  and  instruments  used  for  this 
purpose,  but  all  depend  upon  the  same  principle.  It  is  the 
principle  underlying  all  surveying  and  all  astronomy ; 
indeed  it  is  the  only  possible  principle  for  measuring  a 
distance  when  you  cannot  actually  go  and  lay  a  measure 
upon  it  or  by  it. 

It  is  based  upon  a  peculiar  property  of  a  triangle.  In  the 
case  of  every  triangle  which  has  straight  sides,  if  we  know 
the  size  of  two  of  the  angles  and  the  length  of  one  of  the 
sides  we  can  easily  calculate  all  that  there  is  to  be  known 
about  that  triangle.  We  unconsciously  use  the  principle 
when  we  judge  a  distance  with  our  eyes.  We  focus  each  eye 
separately  upon  the  object  which  we  are  looking  at.  In 
other  words,  each  of  our  eyes  looks  along  a  straight  line 
terminating  in  the  object.  Those  two  lines,  together  with  a 
line  joining  our  two  eyes,  form  a  triangle.  The  line  between 
our  eyes  is  the  "  base,"  the  line  of  which  we  know  the 
length,  while  the  directions  in  which  we  point  our  eyes  give 
us  the  angles  at  each  end  of  the  base.  From  this  we  are 
able  to  judge  the  distance  of  the  object.  Of  course  there 
is  probably  not  one  of  us  who  knows  the  length  of  that 
natural  "  base  "  in  inches,  but  that  does  not  matter  in  this 
case,  since  it  is  always  the  same  whatever  we  may  look  at, 
and  so  the  mere  inclination  of  the  eyes  gives  us  a  means  of 
comparing  distances.  When  we  judge  by  the  eye  alone, 
what  we  really  do  is  to  draw  upon  our  experience  and 
consciously  or  unconsciously  compare  the  distance  which 


MODERN  ARTILLERY  24S 

we  are  estimating  with  some  others  which  we  already 
know. 

In  surveying,  a  telescope  is  set  up  at  one  end  of  a  base- 
line and  pointed  first  at  the  other  end  of  the  base-line  and 
then  at  the  distant  object.  A  scale  with  which  the  instru- 
ment is  provided  gives  us  the  size  of  the  angle  between  the 
two.  Then  the  same  thing  is  done  at  the  other  end  of  the 
"  base  "  and  the  similar  angle  there  is  obtained.  The  length 
of  the  base  being  known,  the  distance  of  the  remote  object 
can  then  be  calculated. 

In  the  same  way  two  observations  can  be  made,  one  at 
each  end  of  a  ship,  the  length  of  the  ship  forming  the  base- 
line. Or  an  instrument  can  be  made  by  which  two  observa- 
tions can  be  made  simultaneously  by  the  same  man. 

This  is  done  by  means  of  mirrors  which  are  turned  so  that 
the  same  object  is  seen  in  both  of  them,  apparently  in  a 
straight  line.  The  extent  to  which  one  of  them  has  to  be 
turned  gives  the  angle,  and  the  instrument  forms  the  base. 

Anyone  with  the  slightest  geometrical  experience  will 
perceive  at  once  that  the  best  results  are  obtained  when  the 
base-line  is  of  considerable  length,  and  hence  small  portable 
range-finding  instruments  such  as  can  be  easily  carried  and 
used  by  one  man  are  necessarily  less  accurate  than  an  arrange- 
ment such  as  has  been  suggested  above,  where  two  observers 
work  simultaneously  from  the  two  ends  of  a  ship. 

In  many  cases,  however,  the  self-contained  instrument  is 
the  only  one  which  it  is  possible  to  use,  and  when  the  instru- 
ment is  well  made  and  in  experienced  hands  the  results  are 
surprisingly  good. 

As  used  in  surveying,  for  example,  where  the  base-line 
may  be  anything,  according  to  circumstances,  and  the 
angles  may  likewise  vary  at  both  ends,  elaborate  trigono- 
metrical calculations  have  to  be  performed  to  arrive  at  the 
desired  result.  If,  however,  the  base-line  be  always  the  same, 
and  one  of  the  angles  be  always  a  right  angle,  the  distance 
of  the  distant  object  will  vary  with  the  remaining  angle. 
Indeed  the  scale  by  which  that  angle  is  measured  can  be 


244  MODERN  ARTILLERY 

made  to  give  not  degrees,  but  the  distance  of  the  object. 
Portable  range-finders,  therefore,  in  many  cases  have  one 
reflector  set  for  a  right  angle  and  only  one  of  the  reflectors 
movable.  The  instrument  then  shows  the  distance  of  the 
object  at  a  glance. 

This  is  impossible  in  the  case  of  two  separate  observations 
on  a  ship.  In  that  case  the  base  is  always  the  same,  but 
since  the  ship  cannot  be  set  at  right  angles  to  the  object 
whenever  a  range  has  to  be  found,  both  angles  have  to  be 
measured.  There  is,  however,  a  beautifully  simple  little 
mechanism  in  which  two  pointers  are  set  one  to  each  of 
the  two  angles,  and  the  distance  is  then  shown  instantly. 


APPENDIX 

A  DESCRIPTION   OF  THE  RIFLES   SHOWN   AT  PAGE  240 

THE   GERMAN  MAUSER  can   fire   forty  rounds   a 
minute — more   than    any    other    rifle    used    in 
the    war.      The    rifle    is    of    the    1898    pattern, 
weighs  9  Ib.   14  oz.  with  bayonet  fixed,  and    is  sighted 
from    219    to    2187    yards.      The    magazine    holds    five 
cartridges,  packed  in  chargers.     As  the  rifle  is  not  provided 
with  a  cut-off,  it  cannot  be  used  as  a  single-loader.     With  its 
long  barrel  and  long  bayonet  it  gives  a  stabbing  length  of 
5  ft.  9  in. — 8  in.  longer  than  the  British. 

THE  AUSTRIAN  RIFLE  is  the  Mannlicher.  This  rifle  is 
very  fast  in  action  as  a  snap  back  and  forth  of  the  wrist  is 
sufficient  to  operate  it.  It  is,  however,  more  trying  for  pro- 
longed work,  owing  to  the  throwing  of  the  strain  only  on  the 
wrist.  Without  the  bayonet  the  rifle  weighs  only  8  Ib.  5  oz., 
the  lightest  of  all,  yet  the  bullet — 244  grains — is  the  heaviest 
used  by  any  of  the  belligerents.  The  rifle  is  sighted  from 
410  to  2132  yards,  and  the  barrel  has  a  four-groove  rifling. 

THE  BRITISH  LEE-ENFIELD — MARK  ni — is  the  outcome 
of  the  South  African  War.  It  is  not  too  long  for  horseback 
and  is  yet  quite  efficient  for  infantry.  The  barrel  is  25  in. 
long  and  has  five  grooves  in  the  rifling.  It  is  sighted  from 
200  to  2800  yards.  The  rifle  is  fitted  with  a  magazine  which 
holds  ten  cartridges  packed  in  chargers,  each  of  which  con- 
tains five  rounds,  so  that  the  magazine  is  filled  with  ten 
rounds  in  two  motions.  The  rifle  is  also  fitted  with  a  cut-off, 
which  enables  it  to  be  used  as  a  single-loader.  It  is  altogether 
a  most  efficient  weapon. 

245 


246  APPENDIX 

THE  FRENCH  LEBEL  is  of  the  1886-1898  pattern,  and  with 
bayonet  fixed  is  longer  than  any  other  rifle.  It  weighs,  with- 
out bayonet,  9  Ib.  3J  oz.  The  tube  magazine  under  the 
barrel  contains  eight  cartridges  ;  it  takes,  of  course,  longer 
to  charge  than  a  magazine  loaded  with  a  charger.  It  does 
not  fire  as  many  shots  a  minute  as  some  of  the  other  rifles  in 
the  field.  The  position  of  the  magazine  is  indicated  by  the 
crosses.  The  rifle  is  sighted  from  278  to  2187  yards,  and  the 
bullet  weighs  198  grains. 

THE  BELGIAN  ARMY  uses  the  1889  pattern  Mauser,  which 
weighs  just  over  8  Ib.  and  is  sighted  from  547  to  2187  yards. 
The  magazine  holds  five  cartridges  carried  in  clips ;  not 
having  a  cut-off,  the  rifle  cannot  be  used  as  a  single-loader. 
It  has  four  grooves  in  its  rifling  and  measures  4  ft.  2 J  in.,  or, 
with  the  bayonet,  4  ft.  11|  in.  The  bayonet  is  short  and  flat. 

THE  "  3  LINE  "  NAGANT  of  Russia  is  |  Ib.  heavier  than  the 
British  rifle  and  is  over  7  in.  longer.  The  triangular  bayonet 
is  always  fixed  and  never  removed  from  the  rifle.  The 
magazine  of  the  rifle  is  of  the  box  type  and  holds  five  cart- 
ridges. The  rifle  is  capable  of  discharging  twenty-four 
bullets  to  the  minute.  A  useful  feature  is  the  interrupter, 
which  prevents  jamming  of  two  cartridges. 

THE  ITALIAN  MANNLICHER-CARCANO  is  of  the  1891  pattern. 
It  weighs,  without  bayonet,  just  over  8  Ib.  6  oz.  and  measures 
50f  in.  The  barrel,  30f  in.  long,  has  a  four-groove  rifling. 
The  box  magazine,  fixed  under  receiver  without  cut-off,  holds 
six  cartridges.  The  magazine  holds  six  rounds,  and  the  rifle 
is  capable  of  discharging  fifteen  rounds  a  minute. 


INDEX 


ACCUMULATORS   or   secondary 

batteries,   65 

Aerial  craft  experiments,  202 
Aerobic  and  Anaerobic  bacteria,  234 
Afterdamp,  228 
Alcohol  as  a  fuel,  49 
Alternating  current,  35,  193 
Altofts,  artificial  coal  mine  at,  139 
Aluminium,  133 
Amalgam,  117 
Ammeters,  25 

Ammonia  in  making  ice,  72 
Ammunition  for  big  guns,  240 
Amperes,  22,  24 
Analysis  and  synthesis,  43 
Anode,  55 
Anschutz,  Dr,  96 
Antennae,  162,  171 
Anthracene  oil,  48 
Arc,  the,  in  wireless,  165 
Argon,  the  gas,  75 
Artesian  wells,  45 
''Atmosphere,"  a  unit  of  measure, 

72 

Atoms,  56 
"Avogadro's  Constant,"  33 


BACTERIA,  beneficent,  234 

Ball  mill,  the,  115 

Battery,  electrical,  23 

Benzine,  45,  48 

Bessemer,  Sir  H.,  236 

Blowpipe,  oxyhydrogen,  120 

Board  of  Trade  Unit,  the,  22 

Boiling  water,  10,  76 

Bore  of  a  gun,  236 

Boulders,  blasting,  20 

Branly,  166 

"  Brattice  cloth,"  224 

Breech  of  a  big  gun,  240 

Brennan  torpedo,  the,  102 

Brewing,  50 

"  Brine  "  in  machine-made  cold,  70 

"  Budding  "  of  yeast,  the,  51 

247 


CALIBRE  of  a  gun,  236 

"  Capacity,"  153 

Capacity  and  inductance,  electrical 
properties,  161 

Carbolic  oil,  48 

Carbon,  n 

Carbonic  acid  gas,  10 

Carburetter,  the,  46 

Cardiograms,  32 

Caselli,  176 

Cathode,  55 

Cavendish,  investigations  of ,  73 

Cellulose,  12,  44 

Centrifugal  tendency,  115 

"  Character  "  of  a  lighthouse,  86 

Charge  and  current,  32 

Cheddite,  13 

Chemicals  in  waterworks,  232 

Chemistry,  organic  and  inorganic,  42 

Chlorate  of  potash,  12 

Chloride  of  soda,  58 

Chronograph,  the,  141 

Clark's  Cell,  23 

Coal  and  oil,  47 

Coal,  burnt,  10 

Coal-dust  an  explosive,  10 

Coal-dust,  explosions  from,  139 

Coal-pitch,  48 

Coal-tar,  48 

"  Coasting  "  lights,  80 

Coherer,  the,  103,  162,  167 

Coke  in  smelting,  125 

Colliery  explosions,  137 

Colliery  explosions,  rescue  appar- 
atus, 226 

Colours  of  the  spectrum,  213 

Colours  of  flowers,  213 

Compass,  a  ship's,  91 

Compressed  air  in  torpedoes,  100 

' '  Concentrates , "  115 

Condensers  in  wireless,  163 

Conservation  of  energy,  132 

Contact  makers,  145 

Coronium,  the  gas,  74 

Corundum,  134 

Coulombs,  23 


248 


INDEX 


Courrieres  colliery  disaster, 
Creosote,  48 
Creosote  oil,  48 
Crooks,  Sir  W.,  33 
Crushing  mills,  115 
Crystal  detectors,  171 
Curie,  M.  and  Mme.,  33 
Curtis  and  Harvey,  9 
Cyanide  process,  the,  118 
Cyanogen,  118 
Cymogene,  45 


221  Electro-plating,  58 

Electros,  60 
Electroscope,  the,  34 
Endosperm,  the,  50 
Engines  driven  by  oil  fuel,  46 
Enzymes,  50 
Ether,  45,  149 
Ethyl  alcohol,  49 
Explosions,  9  ;   in  mines,  137 
Explosive  link,  the,  104 
Explosives  for  guns,  237 


DETECTORS,  167 

Detonator,  the,  14 

Dextro-glucose,  51 

Diamonds,  135 

Diesel  engines,  46 

Direct-current  electric   motor,   191 

"  Dirt-auger,"  the,  15 

Ditches,  blasting,  18 

Drainage,  233 

Du  Pont  Powder  Company,  9 

Duddell,  W.  H.,  37 

Dufay  dioptichrome  process,  219 

Dynamite,  what  it  is,  9,  12  ;  in 
agriculture,  13  ;  firing  a  charge, 
1 6 ;  fruit  trees,  16 ;  marshy 
ponds,  17  ;  ditches,  18 ;  tree 
stumps,  19;  boulders,  19;  wells, 
20 

Dynamo,  the,  65 


"  FALLS  "  in  a  coal  mine,  223 

Fermentation,  50 

Fessenden,  R.  A.,  169 

Field  guns,  241 

Filters  in  waterworks,  232 

Fire-damp,  137 

Firing- pin  of  torpedo,  102 

Flashing  lights,  81 

Fog,  effects  of,  82 

Fog  signals,  88 

"  Fractional  distillation,"  76 

"  Frequency,"  36 

Frequency  meter,  193 

Friction  clutch,  195 

"  Frue  "  vanner,  the,  116 

Fruit  trees  and  dynamite,  16 

Fuses,  firing,  20 


EDDYSTONE  LIGHTHOUSE,  80 

Edison's  accumulator,  66 

Einthoven,  Prof.,  30 

Electric  arc,  the,  123 

Electric  furnace,  125 

Electric  fuse,  the,  16 

"  Electrical  Inertia,"   153 

Electrical  battery,  23  ;  pressure,  23 ; 
cells,  23;  measure,  24;  mag- 
netism, 25 

Electricity,  22  ;  the  current,  56 ; 
electro-plating,  58  ;  purification 
of  metals,  61 ;  secondary  batteries, 
62 

Electrode,  55 

Electrolysis,  55,  170;   in  drainage, 

234 

Electrolyte,  55 
Electrometer,  the,  32,  34 


GALVANOMETER,  the,  27,  170 
"  Gangue,"  the,  112 
Gauges,  208 
Gelignite,  12 

Glycerine  in  explosives,  n 
Gold,  no 
Guiding  lights,  81 
Gyroscope,  the,  93, 100 


HALF-TONE  illustrations,  181 
"  Hard-pan,"  14 
Harris,  SirW.  S.,  36 
Hawke  and  Olympic,  collision  be- 
tween, 198 

"  Head  "  of  the  torpedo,  99 
Heat  and  electricity,  37 
Heat  of  the  electric  arc,  123 
Heat,  testing  by,  205 


INDEX 


249 


Helium,  33,  75 
Hertz,  154 
Howitzers,  241 
Hughes,  Prof.,  159 
Humphrey  Gas  Pump,  231 
Hydraulicing,  112 
"  Hydro-carbons,"  45 
Hydrogen,  liquid,  73 
Hydrometer,  the,  65 
Hydrostatic  valve  of  torpedo,  101 
"  Hyper-radial  "  apparatus,  88 


ICE,  machine-made,  71 

Indigo,  synthetic,  44 

Inductance,  154 

Induction  coil  for  wireless,  162 

Induction  furnaces,  129 

Insulating  ink,  177 

"  Interference  "  of  light  waves,  159 

lonisation  of  the  atmosphere,  172 

Iron,  109 

J 

JUPITER'S  moons,  150 
K 

KELVIN,  Lord,  28 
Kerosene,  46 
Kieselguhr,  12 
Kilowatt,  the,  25 

Kinematograph   in  coal    mine   ex- 
periments, 146 
Korn,  Prof.,  183 
Krypton,  the  gas,  75 


LECLANCHE  cell,  the,  23 

Ley  den  jar,  the,  153 

Light,  speed  of,  151 

Lightwaves,  151 

Lighthouse,  the,  78 

Lighthouse  lamp,  the,  83 

Limit  gauges,  209 

Liquid  air,  73 

Lodge,  Sir  O.,  159,  161 

Lumiere  autochrome  process,  216 


M 


MAGNETIC  detector,  the  first,  168 
Magnetic  pole,  the,  90 
Magnetism,  25 


Magnets,  25 

"  Making  "  light,  the,  79 

Maltster,  the,  50 

Mansfield  Rescue  Station,  the,  224 

Marconi,  161 

Marshy     ponds,     to     remove     by 

dynamite,  17 
Mash  tun,  the,  50 
"  Master  compass,"  the,  97 
"  Master  "  records,  60 
Maxwell,  J.  C.,  152 
Measuring  by  electrolysis,  62 
Mendeluff's  table,  74 
Mercury,  114 

Metallographic  testing,  205 
Metals,  testing,  204 
Methane  gas,  10,  124 
Methyl  alcohol,  49,  53 
Microbes,  their  use,  43 
Mine-laying,  105 
Mine-sweeping,  107 
Molecules,  56 
Morris,  William,  233 
Mud,  gold  from,  122 
Muirhead,  Dr,  167 
Murette  or  pedestal  of  lighthouse 

lamp,  85 


N 


NAPHTHA,  45 

National  Physical  Laboratory,  199 

Natural  frequency,  161 

Neon,  the  gas,  75 

Nickel  chrome  gun  steel,  239 

Nitric  acid,  n 

Nitro-cotton,  12 

Nitro-glycerine,  n 

Nitrogen  gas,  9 

Nobel,  inventor  of   dynamite,   12, 


No'des, 


157 


O 


OHM,  the,  22,  24 

Ohmmeter,  the,  27 

Ohm's  law,  27 

Oil,  mineral,  44 

Oil-producing  countries,  47 

Optical  apparatus  of  lighthouse,  86 

"  Orders  "  of  lighthouse  apparatus, 

88 

Ores,  no 
Orthochromatic  plates,  212 


250 


INDEX 


Oscillations,  electrical,  36 
Oscillatory  circuit,  154 
Oscillograph,  Duddell's,  39 
Oxide  of  iron,  133 
Oxyacetylene  flame,  the,  131 
Oxygen  gas,  10 
Oxyhydrogen  jet,  130 


PARAFFIN  wax,  45 

Patents,  174 

"  Periodicity,"  36 

"  Personal  equation,"  the,  207 

Petrol,  45,  52 

Petroleum,  44 

Phonograph,  the,  60 

Plans  of  a  ship,  199 

Plates  of  the  secondary  battery,  64 

Platinum,  184 

Plumbago  in  plating,  59 

Poulsen  arc,  the,  173 

Poulsen,  Valdemar,  165 

Pressure  gauges,  143 

Priestly,  investigations  of,  73 

Primary  colours,  213 

Prisms,  reflection  of,  85 

Process  blocks,  186 

Projectiles,  velocity  of,  237 

Propellers  of  the  torpedo,  99 

Propellers,  testing  aerial,  203 

Prout's  anonymous  essay,  74 

Prussiate  of  potash,  177 

Purification  of  metals,  62 


Q 


QUADRANT  electrometer,  the,  35 
Quartz,  113  ;  fibre,  31, 131 


RADIUM,  33 

Ramsey,  Sir  W.,  75 

Range -finding,  240,  242 

Rayleigh,  Lord,  74 

Receiving  instruments  for  wireless, 

162 

"  Record  "  vanner,  the,  116 
"  Rectifier,"  the,  37,  171 
Red  rays  of  light,  82 
Reflection  by  prisms,  84 
Reflectors,  lighthouse,  84 


Reiss  electrical  thermometer,  36 
Repeated-impact  testing  machine, 

204 
Rescue  teams  for  colliery  accidents, 

221,  222 

Resistance  welding,  126 
"  Resonance,"  an  experiment,  160 
Reviving  apparatus  for  coal  mines, 

229 

Rheostat,  the,  188, 191 
Rhigolene,  45 
Rifling  of  a  gun,  239 
Rubber,  synthetic,  44 
Rubies,  artificial,  131 
Rudders  of  a  torpedo,  100 
Rutherford,  Prof.,  33,  168 


SACCHARINE,  48 

Saltpetre,  12 

Schwartzkopff  torpedo,  the,  99 

Scilly  Island  lighthouse,  80 

Sea,  gold  in  the,  120 

Secondary  battery,  the,  62 

"  Sectors,"  81 

Selenium,  184 

"  Self -rescue  "  apparatus,  a,  228 

Shale,  oil  from,  45 

Shells  for  guns,  239 

Ships,  testing  by  models,  200 

Short  circuit,  179 

"  Shunt,"  the,  165 

Sighting  a  big  gun,  241 

Silica,  133 

Skating  rinks,  ice  in,  71 

"  Sludge  "      and      "  effluent  "      of 

drainage,  233 
Spark  detectors,  166 
Spark-gap,  162 
Spectrum,  the,  213 
Spinthariscopes,  33 
Spirits,  52 

Springs,  testing,  203 
Stamps  for  crushing  quartz,  113 
Starch  grains  in  colour  photography, 

217 
"  Step-down  "      and      "  step-up  " 

transformers,  127 
"  String  galvanometer,"  the,  30 
Submarine  mines,  104 
Submarine  telephone,  88 
Sulphuric  acid,  n,  43 
Sunlight,  composition  of,  213 
Synchronism,  difficulties  of,  182, 191 
Synthetic  substances,  44 


INDEX 


251 


"  TAMPING,"  15 

Tank  fortestingat  Teddington,2oi ; 

New  York  harbour,  201 
Telautograph,  the,  180 
Telectograph,  the,  180,  185 
Telegraph  key  for  wireless,  162 
Telewriter,  the,  187 
Temperature,  measuring,  38 
Tesla,  Nicola,  164 
Testing  by  heat,  205 
Testing  machines,  206 
Thermit,  135 
Thermo-couple,  the,  38 
Thermo-galvanometer,  the,  37 
Thomson  Mirror  Galvanometer,  the, 

28 

Thomson,  Prof.,  S.,  159 
Torpedo,  the,  98 
Training  station  at  Forth,  225 
Transformer,  the,  127 
Transmitting  instruments,    163 
Travers,  Prof.,  75 
Tree  stumps,  blasting,  19 
Tuning-fork  a  standard  of  speed,  193 
Turret  of  a  battleship,  240 

U 

ULTRA-MICROSCOPE,  the,  209 
Ultra-violet  rays,  172 


Veins  or  lodes,  113 
Vickers,  202 
Voltmeter,  the,  26 
Volts,  22,  24 


W 


WATER  a  source  of  heat,  124 
Water,  soft  and  hard,  232 
Watt,  the,  24 
Waves  caused  by  ships,  recording, 

200 

Wax  models  of  ships,  199 
Welding  by  electricity,  125 
Wells,  blasting,  20 
Welsbach  mantle,  the,  124 
Whitehead,  99 
Wire  guns,  238 
Wireless  telegraphy,  161,  173 
Wireless  torpedo,  the,  102 
Wood-meal  in  explosives,  12 
Wood  spirit,  49 
"  Working  fluid,"  the,  68 


YEAST,  51 


VARLEY  and  the  Atlantic  cable,  28 
Vaseline,  46 


ZERO,  68 

Zinc  in  gold  recovery,  119 


THE   RIVERSIDE   PRESS   LIMITED,   EDINBURGH 
1917 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below, 
or  on  the  date  to  which  renewed.  Renewals  only: 

Tel.  No.  642-3405 

Renewals  may  be  made  4  days  prior  to  date  due. 
Renewed  books  are  subject  to  immediate  recall. 


RCC'DLD    APR  1872-ttPM 

' 


Y.C  i  02545 


